I thought I'd make a couple of clarifications that might help. If you're already aware, sorry about that (but hopefully it will be helpful to other readers, too).

First, I think you're referring to primary and secondary enchants here. Primary enchants are marked with a bright, solid blue square, and secondary enchants get a duller, dimmer blue square. (For completeness' sake, the bronze-colored enchants on relic, archeotech, and ancient gear are called "relic enchants" and the green-colored enchants on morality gear are called "morality enchants").

Second, I may have missed it in your post, but you actually can change the mix of primary and secondary enchants on an item by using the "re-roll all" button in the crafting interface. This randomly chooses a new mix of primary and secondary enchants, but does not change the total number. It also randomly re-rolls all of the enchants themselves. This can be an admittedly expensive strategy, but for end-game items, it's not uncommon to do this a couple times to get your desired mix.

  I should point out that not all mixes are possible. There are minimum and maximum numbers of primary and secondary enchants that can exist on an item, but unfortunately, the min's and max's depend on both the item rarity (relic/archeotech/morality) and also the total number of enchants (4/5/6). In addition, the probability is not uniform, so you have a higher chance of getting a mix than you do all of one type (if that is even possible with your specific item). The math behind how the mix is chosen is a little complicated, but as a rule of thumb, it's generally easy to get several primary enchants and at least one secondary enchant. To give a concrete example, for a relic-quality item with 6 total enchants, you are guaranteed to get 1 relic enchant, 2 primary enchants, and 1 secondary enchant. For the other two enchants, one has a 60% chance of being primary and 40% to be secondary, and the other has a 30% chance to be primary and 70% chance to be secondary. As I mentioned before, these guarantees and probabilities are different depending on the item rarity and total number of enchants.

Anyways, my personal feeling is that I've not had too much trouble rolling end-game items with the exact mix and type of enchants that I want. Sure, it's expensive, but it's also about the only real currency sink in the end-game, so I don't mind so much. I understand your experience may be different, and I think it's good to hear a mix of opinions, so I'm not trying to diminish your point of view.

As for your specific suggestions, I have a couple thoughts in response.

For (1), while I think this might be doable, I think it would also probably be necessary to make the cost scale non-linearly with additional levels. While this means it would be possible to squeeze an ilvl 83 item to ilvl 90, the cost of taking an ilvl 53 item to 90 probably has to be prohibitive, otherwise the loot system becomes even more of a vendor-everything-because-only-credits-are-worthwhile thing, and that probably isn't healthy. In addition, I'll point out that ilvl 91 to 100 items are still drop-only, so really end-game items are still beyond item-level upgrading.

For (2), it sounds a bit too easy to selectively choose whether an enchant slot is primary or secondary, again, largely because it takes away from the 'drop' aspect of the ARPG, which is normally an area that you want to keep interesting. This is actually the same reason I'm torn on having the total number of enchants be modifiable. While I agree that it's frustrating to get a great drop that only has 4 enchants, it would also mean that you'd only ever need a single relic-quality item drop. That seems a bit extreme. One potential compromise here would be to consider a mechanism for changing the number of total enchants on archeotech and morality rarity items, since the relic enchant on these items is locked in. That still means there's a "chase" aspect of looting end-game items, since you'll might be hunting for a specific archeotech enchant, but it also reduces the immense feeling of wanting to bang your head into a wall when you actually get that enchant you've been searching so long for, only to have it on a 4-enchant item.

For (3), again, I think the proposal is a bit too easy (a lack of randomness generally leads to a fairly dull-feeling loot system), but I understand the frustration you're feeling. One alternative approach would be to cull a good chunk of the truly useless enchants that are polluting the enchant pool in some areas. It's one thing to fish for an enchant among a pool of 10 or even 20, but it's a very different feeling when you're fishing in a pool of 30, 40, or more. Eliminating bad enchants would tone down some of the worst offenders while still giving the item crafting system some non-determinism.

Anyways, I hope this clarifies some things, and I'd welcome your thoughts on the matter if you have them. Thanks!

I'm curious though. You point out that the loot system might become even more of a vendor-everything thing. Can you elaborate on that? I must say that in the end-game I never find anything worthwhile at the vendors.

Sure, this is my mistake for not being more clear. What I meant by "vendor-everything" was that there would be less incentive to look at or keep any item drops you collect. This is ultimately one of the trade-offs with any crafting system. If it becomes sufficiently powerful, then all you really need is a single item and sufficient crafting fuel to mold it into what you need. The problem with that is that the core gameplay loop (run-shoot-loot) loses diversity and flavor in the "loot" part---since everything that drops would simply be various amounts of 'crafting fuel'.

I definately need to try to get more morality items.

There are some that can be fun, but IMHO most are not particularly strong for how difficult it can be to farm specific ones. I would definitely not try to craft a build around a specific one, since you're likely going to play most of the game without it. Still, no harm in playing around with them if you get them. The nurgle spawns are a particularly amusing favorite, even if the enchant itself is not all that strong.

May I ask you if your gear is of mixed rarity (relic, ancient relic, archeotech, morality)?
I'm just curious because my gear is all relic, ancient relic and 1 or 2 archeotech.

That's a pretty typical mix, in my experience. In fact, I'd argue that the *reason* it's a typical mix is precisely *because* of the strength of the crafting system. Relic items are cheap and easy to reshape into finely-optimized pieces, so they become the mainstay of your equipment. I usually mix in a few ancient items as well, mostly to take advantage of an enchant that cannot normally appear in that item slot (ancient items do not have to abide by any of the normal item rules, since they are completely hand-crafted).

It feels archeotech can be really strong but the drops are very rare and finding that 1 item that you feel you can use to upgrade your build.

This sounds accurate to me. Archeotech items aren't always better than relic items across the board, but there are definitely many which are substantially better, and they're worth farming for. But you're right that it can certainly take a while. (And as I mentioned in the response to your third suggestion, it can definitely sting when you finally get that archeo enchant that you've been looking for...and it's on a 4-enchant item).

Maybe I should use more often a tarot and seal combination to up the drop rate for specific gear, combined with a tarot for more archeotech or relic drops. Have you ever done that and did you feel it makes a significant contribution to finding good gear drops?

You could do this. I think the more common approach is to slot loot quantity (and to a lesser extent loot quality) into secondary enchant slots in your gear. Secondary enchants can be surprisingly powerful, and +XP (while leveling) and loot enchants (afterwards) are definitely a core part of that. The difference between a character with no loot stats and one running them in all the available slots they appear on is absolutely noticeable. In fact, some players have started observing that if they stack too much on high difficulties, you literally cannot loot everything that drops in a single run. So I'd definitely recommend at least some loot enchants if you're at or near level 100.

I'm glad you feel a rekindled sense of interest in the loot system, and I wish you the best of luck in your drops!