Alex Henrie [off-list ref] writes:
1. Add a --no-rebase-merges option to `git rebase`.
2. Add a rebase.merges config option.
3. Add a warning to `git rebase` that appears if rebase.merges is
unset and neither --rebase-merges nor --no-rebase-merges is given. The
warning would advise the user that the default behavior of `git
rebase` will change in a future release and suggest setting
rebase.merges=no-rebase-cousins to get the new behavior now.
4. Change the `git pull` advice to recommend --rebase=merges and
pull.rebase=merges.
5. Wait a couple of releases.
The above sounds like a standard "flip the default" dance executed
in the usual order. I am not sure about the remainder but that is
not because I find anything wrong in it, but because I haven't
thought things through that far into the future ;-).