Here is the list that I've arrived at that was working okay - but obviously very unoptimized. It's a little dumb to say, I guess, but essentially, if I drew 2 or more Tasha's, I almost certainly won, and won fast if I didn't, I struggled or lost. With both of these decks combined, at 18 games in, I'm at exactly a 50% winrate in mythic. For the Azorius deck I went a lot more heavily into bouncing - I took ] along with ] to try to clear the board in a different way (though I definitely am still running Doomskar). So, I swapped to Azorius, and had about the same luck, on a much larger sample size. With Dimir, I found I was getting run over too much - it could have just been the games on a low sample size, but I felt like I really wanted a doomskar and some life gain. So far, I've tried it briefly in a Dimir Control shell, and an Azorius tempo shell. I think there are potentially several shells that can make it work, but I don't think I've quite found it yet, and I'd love some help from the hive mind that is r/spikes to see what we can do here. I feel like with ] and even ], mill should be a real threat right now.
That's a whole lot of mill for just 3 mana. I've seen it roll as low as 7 before on a ramp deck where it hit an alrund's epiphany and a few other big value cards, but often I see it hit more in the range of 10-15. Because Tasha's essentially doesn't have a limit, I think there's a ton of power there - I've seen Tasha's mill as many as 20 cards on an aggro deck before - and any card that sometimes says 'pay 3, opponent mills 20' has my attention. So currently, we have two extremely powerful mill cards in the format in ] and ].