I blogged about this recently in a post https://popey.com/blog/2021/03/ubuntu-wiki-reboot/
I agree. In my opinion we should create a new wiki, which still uses Ubuntu SSO for sign-in, and has anti-spam measures. It should have enough resources to not be slow and painful to edit like the current wiki (this is a given). A page structure and style guide should be available on launch. The old wiki have a big banner redirecting to the new one, and at some point (after 3-6 months) be made read-only, eventually to archived, with redirects from old pages to new. I’d also merge both the wikis you mention into one.
The community could help in migrating pages from the old to new wiki, and focus on pages which are heavily visited, heavily used or deemed of historical importance.
This needs Canonical IS involved. Or the guerrilla approach, someone in the community could just stand up a MediaWiki on a new domain, configure spam protection and SSO, and get started without having to wait on IS. Maybe do that on a domain which isn’t spidered by robots, and then when IS have time, hand over the site / database and get them to host it.