It's just the add-on title seems to be what is already the current situation.
I see what you mean
The title "remove-nofollow-from-admin-mod-urls" suggests that nofollow is removed for admin/mod signatures. This is existing Xenforo functionality.
I think it's just the title that of that thread that needs updating...
[I'm still using my modification for now, until I look into it]
The suggestion was to give the option (from the ACP) for all members to have non no-follow links. Some forums really trust/appreciate/need the content from their contributors. Links (without nofollow) is a good way to reward these site, and I think the philosophy behind these links is a good one
If I've written 10,000 posts on a forum all about "quantum mechanical tunnelling"... Well if I wasn't an expert at post 1, I'm pretty certain I will know quite a bit about the subject by post 10,000
(I could cram my entire Edinburgh Uni Chemistry Masters in about 2 weeks worth of forum posts)
So gaining links from relevant forums should increase your back links (without nofollow), because the more you communicate about your subject, the more you become an expert, the more your site should be an authority on the subject.
In some peoples opinions backlinks are phasing out (I don't wish to go off topic, this is discussed all over the web) but I still think some forum owners want to give something back to their forum members.
It would be nice for Xenforo to provide this option, instead of giving all non admins / mods "no-follow" links, even in their signatures.... (not all forum communities are riddled with spam 'SEO' hired 'link builders')