It would require the celestial main chain to have some sort of execution environment. But it's also, if you do trade on those roll ups, you could move whatever equivalent into a theorym and then off to another roll up. To me, i see them as floating, not on ethereum, but like kind of floating in space, just connecting a lot of these othernoe makes more sense. I think these bridging providers would rather be their own chain, or something on etherum, or, i don't know, the agnostic.