There is no ETA on 1.0, but breakage has followed the pattern of it not really being hard to upgrade to a newer version, as it is very well documented on the version release notes.
writergate was not smooth, a lot of things that moved over to writer (Writer.Allocating for instance) had no documentation and I had to go read the zig source code to figure it out. the docs were just "instead of That use This"
Yep. He mentioned recently in his JetBrains interview he wants Zig to be a language for the next 50 years. Rushing 1.0 for the sake of signaling to the wider industry today would be actively harmful to that goal.