The only thing that's clear is that Sukuna has to do something himself to be able to survive this because neither Ura nor Kenjaku stand a chance against Gojo. Yeah he's probably nerfed but imo he's still not nerfed enough for anyone bar Sukuna to be a threat to him. Let's be fr, Gojo could use Blue to teleport his ass away and recover a lil while Yuji and co stall Ken and Ura enough for him to recover (if he's truly that fucked up). Then he teleports again back and gives them a one sided beating. Point is, if Sukuna doesn't take out Gojo it's over for the manga itself.
Regarding Sukuna, Open is the best option because you know how shonens are; the author can make an unknown ability do whatever the fuck he wants lol. It's cheap but well, shonens are like that.
I don't believe on Maho's adaptation for several reasons. 1. If Sukuna barely started using it, then he only adapted to Purple. Everything else is still a (big) fucking problem including the main ability; passive infinity. 2. The one that adapted to those things that are a problem (red, blue, UV and infinity) is Maho who is now dead which means that Sukuna has to do the painstakingly process of adapting again. This can be solved by moving the adaptation from Maho to Sukuna himself but isn't that an asspull too? And the same thing with Open is happening right now. Gege taking advantage of the fact that we still don't know everything about an ability to do whatever the fuck he wants.
He can either:
1. Since we don't know what his TCT is, he could have anything then, maybe even something to bypass Infinity.
2. Since Sukuna is the best TS user so far and we don't know the upper limits of it, he can make the TS achieve any effect that he wants