@evouga are we even talking about similar decks when considering one or the other? This feels much more a control card than Citadel. Also, I disagree that Citadel is easier to cast than this. Citadel needs either Rituals or Tinker.
That's a fair question. I think the value Elsha provides is too marginal and the hoop too high to be attractive in a control shell... I'd worry you'll quite commonly hit a glut of lands or countermagic.
Also resolving Tinker is arguably easier than casting 2URW
Hrm I'm still more excited by Bolas's Citadel, I think.
Citadel is one mana more expensive, but in far less annoying colors, so you're probably looking to cheat Elsha into play. You have to pay mana for the spells you chain, which is a big minus compared to Citadel, and in return Elsha is a win condition on her(?) own (assuming you want to wait a turn to remove summoning sickness, which you probably do not) and the Flash ability gives you a bit of resilience to countermagic, since you can keep casting spells in response to any of the opponent's counterplay.
Apparently WotC thinks this card is Vintage-playable: https://magic.wizards.com/en/articles/archive/play-design/m-files-core-set-2020-white-blue-black-2019-07-12
Interested to see what happens with this in Vintage. It will certainly get attention. Six-of VT is worth a build-around.
That's certainly a quaint take on the format