My only issue with SMF and it's future is the mindset of individuals 'owning' their mods, to the point where no one else is allowed to contribute to them. As opposed to the mods being a contribution to the community. I think this attitude really hurts SMF and anyone who uses SMF. In this regard, SMF may embrace the open-source license, but not the spirit. As a result it is very hit or miss as to whether a mod gets updated to the latest version of SMF, or whether you'll get any help with a mod an author may have lost interest in.
Compared to Nucleus CMS, Nucleus encourages an atmosphere of open source plugins. And in this regard is the polar opposite of SMF. Quite often a plugin will be updated, or support given, by someone other than the original author, when the original author is no longer interested. Sometimes even when the original author is still active, someone else will post some improvements on or even a complete rewrite, though usually this follows a discussion in the forum. The wiki, the official source for plugins, is editable by anyone. No approval needed to submit code or change someone elses code.
I have less experience with FluxBB but Flux seems to be somewhere in the middle of these two examples, mods are not usually changed without the authors permission. Approval is needed to submit a mod, and you can't change someone's code in the repository, but there is little evidence of the 'this is mine and you can't touch it' mentality.
From what I have seen of Wedge, I suspect it will be even more of a 'locked down' community than SMF, though I haven't really been following it closely.