The latest spoiler from Rivals of Ixalan looks like this:
Let’s try to evaluate that. Let’s start with the base. How good is the card without the City’s Blessing ability?
We have some options in Standard. [scryfall]Trial of Ambition[/scryfall] forces an opponent to sacrifice with only two mana, but is sorcery speed. [scryfall]Perilous Predicament[/scryfall] is an instant and gets rid of two creatures, but is much more expensive.
Also, we have to note that neither of these see any play currently. [scryfall]Doomfall[/scryfall] on the other hand does, as you can target the player and their hand, if there aren’t creatures around. It has the added benefit of being able to get rid of [scryfall]The Scarab God[/scryfall] permanently.
Based on that, [scryfall]Vona’s Hunger[/scryfall] is not going to be good enough. How about the Ascended version than?
If you have ten permanents on the battlefield, it wouldn’t be out of the question for the opponent to have that many as well. How many of them are going to be creatures? Half? In that case you would get three of them, which isn’t exactly bad, although they are the worst of their creatures.
On the other hand, if your deck is dedicated to Ascending, your opponent’s might not be, in which case you might have various random things, such as 1/1 Servos and Treasures lying around, while your opponent has a [scryfall]Glorybringer[/scryfall] pushed out early through a [scryfall]Servant of the Conduit[/scryfall]. In that case, you would get the Servant, in which case you probably would have rather used a [scryfall]Fatal Push[/scryfall].
There is definitely a Magical Christmas Land scenario, in which your opponent attacks with their two [scryfall]Glorybringer[/scryfall]s, while leaving back two blockers in a racing situation and when you use this mid-combat, they know they have to sac the dragons, because otherwise they’ll be dead on the swing-back. How often is this going to happen?
One interesting case here is competing Hungers. What if both sides have one and are ready to Ascend? Then, whoever casts their’s last wins, because the opponent can’t Ascend anymore (or might be unable to, your mileage may vary).
In limited it might do some work. Removal isn’t often plentiful, so you might have to play it and sometimes it might even be very good.
Ascend, as a mechanic, might lead to some interesting situations, where you can bluff certain things. So, don’t trust anyone who keeps counting their permanents just a bit too visibly.