Yeah, git-meta is a reasonable alternative to megamonorepos. It's basically a repo-mega-forest.

A few things:

  - your build system will need more code
    to deal with a repo-mega-forest than
    a megamonorepo
  
  - code indexers may not be able to see
    cross-repo dependencies

etc.

You'll have pain no matter what. My preference would be for a megamonorepo approach to scale properly. That means partial/sparse cloning, as well as shallow cloning, and also all the hacks that are supposed to make git-status and git-log (and git-blame, and...) fast in partial clones.