Related, but somewhat different to this idea:
It’s odd that Create Topic allows posting to groups, even if you’re not a member, but that you can’t reply to group topics unless you’re first a group member.
I don’t want to lose the ability to post to a group without being a member (core part of our UX and the simplest solution, imo), I’d just like to allow others to reply if they’re not a group member.
Candidly, the other idea is a better solution because it will drive group and community sign ups. However, the limitations on replies is our #1 FAQ and this might be a quicker fix.