It definitely is ambitious! A multi-year effort.
This post https://www.unison.cloud/our-approach/ talks more about why such radical changes were necessary to achieve what we wanted. (In particular check out the "3 requirements of the dream" section, which walks through what the programming language needs to support to be able to do things like "deploy with a function call.")
My general take on "when and where to innovate" is: if you can get a 10x or more improvement in some important dimension by doing things differently, it can absolutely be worth it. This is the philosophy we've applied in developing Unison over the years. I am generally happy to learn something new if I know that I'll be getting something substantial out of it. Of course it can be hard to tell from the outside if the benefits really are worth the changes. I'm not sure what to say about that, other than try it out with something low risk and decide for yourself.
Besides the distributed programming / cloud stuff, I'll give a couple other examples where we gain advantages by doing things differently: by storing Unison code in a database, keyed by the hash of that code, we gain a perfect incremental compilation cache which is shared among all developers of a project. This is an absolutely WILD feature, but it's fantastic and hard to go back once you've experienced it. I am basically never waiting around for my code to compile - once code has been parsed and typechecked once, by anyone, it's not touched again until it's changed. This has saved me countless hours compared to other static languages. And I don't have to give up static typing to get this.
This sort of content-addressed caching also plays out for testing - for pure tests (which are deterministic), Unison has a test result cache keyed by the hash of the test code. This also saves countless hours - imagine never needing to rerun the same tests over and over when nothing's changed! (And having certainty that the cache invalidation is perfect so you don't need to do a "clean build just to be sure")
Also replied here re: self-hosting https://news.ycombinator.com/item?id=39293568