I've been monitoring this for a while now, and for our community to move from Collabs to Clubs, here's what we'd need from IPS or another provider:
Support for Pages. Our Collabs write a lot of things that should be "articles," and it's pointless (and burdensome) to just overuse pinned posts for this.
Support for Databases. Same thing - our Collabs develop a bunch of different databases for their own content, and rather than create those at the global scope, we'd like to see them moved to the Club scope.
More than 3 member levels per Club. We leverage this to set (and advertise) ranks within our Collabs, and having a flatter 3-tier approach will make it harder for us to recognize people who step up and lead within our (very large) community. This also ties in with point 5 below.
Conversion from Collabs (obviously).
Support for badges. I wrote this for Collabs (see link below) and would be happy to write the same for Clubs - I just haven't looked into what it'll take yet as we're not in a position to leverage Clubs just yet.
https://invisionpower.com/files/file/7815-group-collaboration-badges/