Branch structure to maintain 3.x and 4.x simultaneously

That sounds like something that could be improved upon. If they can import their whole workspace, that sounds much easier.

Sure, there is a lot of room to streamline that.

Close?

Yes!

An official, fleshed out, version of that along with what features are tied to what aspects of the serialization format could be interesting, but I wouldn't spend a ton of time on it, because it's just a proxy for the implementation, which is the important thing to review.

Ok, I'll draft something small then.

I certainly hope we don't get to that point. I hope that we continue to "rescue" functionality from the Delta branch and merge it into master. I'm willing to help with that effort.

Great, thanks a lot! I think it's an exciting challenge too.

I'll start a separate thread about breaking change scheduling.