There are a lot of things to untangle here!
Is it possible to use a variety of dice types in various combinations to get PbtA-style results, in a single roll? Absolutely. I’ve written several games that do this, and it works really well. For example, my game The Bureau uses this idea exactly like that - the probabilities are absolutely perfect for this kind of application:
There are lots of fun ways to do “combined die types” with PbtA-style moves, and the math is just perfect. Like I said, I’ve used this in a variety of designs. I actually use this kind of hack when I play Apocalypse World and similar games - you get one die based on your character’s state, one based on their ability, and one from the GM, based on your circumstances. It’s lovely, and it’s great because there is no math to do. (Note that I do not use dice quite as large as IaWA’s, though - a d12 would be an enormously powerful die in this hypothetical system, like a +4 in normal PbtA parlance.)
Your idea of rolling two dice and matching (or not matching) with an opposed roll has also seen some use, like, I believe, in Ironsworn (I’m not familiar enough with the game to be sure, but it sounds like exactly that, from what I’ve read - e.g. https://phophosolo.home.blog/2019/01/10/basic-probability-in-ironsworn/).
Having said all that, the format you are considering isn’t applying the basic principles of In a Wicked Age…, which are really important to that game and the design. Simply grabbing those Forms isn’t necessarily going to make for a good game.
First of all, the game design depends very heavily on the subjectivity of the Forms: you see, choosing your strongest Forms in that game is not a smart long-term move (since it takes you out of the running as a long-term protagonist). Playing with your weakest or strongest Forms is a big part of what allows each player to decide whether they are playing an underdog hero or a terrible villain we’ll never play again. Without this piece, you’ll likely find the Forms to be too “loose” for any kind of play which doesn’t expect the characters to succeed more often than not (since, without the We Owe List, there’s no incentive not to use your best Forms all the time, and they tend to be subjective enough that you can grab them almost whenever you want - how hard is it to justify rolling “For Myself”, for example?). In IaWA, though, that’s a meaningful choice all the time, because of the Owe List.
The Owe List is the most important design feature of IaWA, and you have to find a way to make it work with your hypothetical hack. It provides long-form structure and the necessary counter-balances for the Form choice to work in the first place.
So, what’s your goal? To redesign IaWA with some PbtA mechanics (I have a draft for this somewhere, actually…)? In that case, you need a clever solution to the Owe List under this new hacked design. Or is it to use IaWA Forms in regular, PbtA adventure play (with no Owe List)? In that case, you’ll need different Forms (and possibly different die sizes).
I hope that’s helpful! As you can tell, it’s something close to my heart: I’ve given this a fair bit of thought.