Either the talk Code is the easy part or the post What is “constructive” input?. I don’t know about anything else that comes close to an official statement.
Sadly not.
As long as Elm is in its beta, this will probably not change. The reason for it is that Evan wants to try out different things and also allow breaking changes without needing to listen to the community. We have seen it happen with signals in 0.17. I believe this was for the better. So personally this does not necessarily need to be a bad thing.
There are a few people around Evan that are considered core contributors. I would assume that in that case one of them would take over.