Personally speaking I’m not relying on white-box macros so much, so here I’m focusing on black-box macros here because white-box macro discussion is already there Whitebox def macros
My point is even if the functionality of the black-box macros will be maintained, interface change might happen for better language design (and I think this should occur if it will be more usable). Then cross-building Scala 2.12, 2.13, and 2.14 (with new macros) will be necessary for a while. During the migration, we will be able to find some potential problems in the new design. So I think having a list like https://github.com/sbt/sbt/wiki/sbt-1.x-plugin-migration is good.
Yes. Having a gitter channel would work as well.