There will be pressure to make it easier to discover plugins, install plugins, install plugin dependencies, manage plugin options, uninstall plugins, verify and validate plugins, etc. It's all well and good to punt these problems to 'someone else' but that usually means either no one, someone who does a one-shot that becomes immediately out-of-date, or someone nefarious.

The project mono-repo is the way to go. Long-term maintenance is the primary software challenge, and distributed maintenance is strictly more difficult. If the project truly has hundreds of motivated contributors, then forks or plugins might be worthwhile, but most projects struggle to keep more than one motivated contributor.