I think slimytrout does bring up a good point though about the value. Maybe we could go through and basically account for the extra value by pricing rift costs a little more than improvise because it "costs" less than improvise does in terms of boardstate? In other words, we just say, ok
Metallic Rebuke was three mana, so maybe we make the rift version 4 because it is less of a drawback to cast it with your enchantments.
I think we could search around for another mechanic, but I can't shake the feeling that rift might work for what we are doing here. I've been really trying to come up with alternatives but so far I can't think of many other options we can go with. I know rift has its problems, but I'm not sure we have a better solution at the moment. I'd definitely be willing to swap it out with a different mechanic if we think of one as time goes on but for now I think it might be our best bet.
I'd love to windmill slam something like constellation into the set, but I think staying away from Theros is a definite factor. I think rift isn't particularly exiting, but I think it will work pretty well with Glorify, especially if we cost it approximately. I think the set just needs a kind of "boring" mechanic that rewards the player having lot's of enchantments and I don't think there are too many good options in that space. Without something like constellation or improvise, there is no real incentive to build enchantment matters decks imho.
Where I think we can make up ground is with the fourth mechanic. It can be the unique and cool mechanic, that also smooths out the bumps of the set. To be honest, I tried my best to come up with a replacement for rift, but, and maybe this is just because I'm not particularly inventive, so far I don't think I've had any better ideas. That might just mean we need a fresh perspective, but I think testing it out might yield some good results.
As far as the fourth mechanic goes, I think we want something really really original. To me, I think this set's mechanics so far score really high so far on fun, balance, and practicality, but very low on originality. Which is kind of my fault for pushing a version of improvise. But, I do think if we go big with the fourth mechanic, and do something very different and unorthodox, that will shore up the set nicely.
I think this set might play out really well. I'm going to try and make a bunch of test cards like the crazy guy I am and do some goldfish drafts with them to try and get a feel of how things might shake out in games of limited with these mechanics combined.
To back up my claim, I think Kaldheim is a good example.
Kaldheim had
MDFCS
Snow
Sagas
Foretell
Boast
(Runes, but it was only five cards so...)
Changeling
Changeling is a return
Snow is a return
Sagas is a return
Foretell is new, but it combines morph and suspend.
Boast is new, but is basically tweaked Raid.
MDFCs were new but were a return by the time they showed up on Kaldheim.
So if we use rift we have
Glorify/Favors, is new but has aspects of learn/lesson
Rift, is new, but is tweaked version of Convoke/Improvise
Exalted is a return.
????? One new mechanic that hopefully brings some spice to the set and makes it really stand out.