Discussion at https://en.wikipedia.org/wiki/Wikipedia:Page_Curation/Suggested_improvements#Remove_userspace_from_Special%3ANewPagesFeed%3F
We can either turn this off by
1) modifying $wgPageTriageNamespaces, or
2) by stripping it out of the code entirely.
#2 might be better because it reduces complexity of the software, which is good for maintainability. So for example, we could remove namespace 2 from extension.json, and we could delete the MFD code from delete.js.
A one time SQL delete query might need for pagetriage_page and pagetriage_page_tag entries for pages in namespace 2 (user).
I see the primary benefit of this as not encouraging patrollers to use limited patrolling bandwidth to patrol a namespace that doesn't need patrolling. There are also some technical benefits, such as reduction in SQL table sizes and simplification of the code.