Essences : they were arguably Season 5’s main and most game-changing feature.
Attack Seru
Fine as it is.
I’d rather jitter were gone altogether (such an awful game design element), but this is the next best thing.
Ultos
With Attack Seru removing the need for multiple copies of the same item, I like the fact that this provides a new use case for said multiple copies.
You’ve already said you were reworking the affix list, so no need to expand on that.
I’m not sure it should work on Epics, though.
And, contrary to the majority feedback you got, I’m positive it should not work on rares and MIs.
In case they were made craftable, use Celestial Essence as the base component.
Vire
By far the least useful of the lot. Actual use cases are few and far between, especially in 1.2 where “farming” a higher version of an item is super easy (except for non-boss MIs, but those are supposed to be shoppable, aren’t they ?).
I suspect they’re the main reason people have asked for an essence conversion mechanism.
I don’t mind them being there, but in all honesty, I’d just remove them.
Ishtak
Far too random.
I think I would have Ishtak be “Ultos for Epics”, but that’d be more work for you.
Essence containers and Affix Reroll essences
I’ll go with an unpopular opinion here : essence containers should be more prevalent, and affix rerolls essences should be removed.
The idea was, I suppose, that when a rare drops with a nice affix, you reroll the other affix and then transfer the lot to the desired item.
Except we spend most of our time in scalable dungeons, where you can’t sell items and use the shop’s search function. Parsing tons of items on the floor is a hassle in those conditions, so in the end, you just craft for one affix, and reroll for the other.
Loot gets ignored.
I find it a tad ironical that you nerfed shops, and held your ground against the negative feedback of your player base, because you were adamant that items should be looted and not shopped… and then you implemented a feature which made loot obsolete. 
Loot / Affix Transfer / Affix Reroll
=> pick two
I believe that no rerolls but “free” transfer to be the best combination : it gives the player some agency about customizing their items, while keeping loot important.
I know, especially with Crate announcing their own rerolling feature, that you’re unlikely to go in the direction I’m pointing, but at least I’ll have stated my case. 