We're transitioning from a SVN monorepo to Git. We've considered doing a kind of best-of-both-worlds approach.

Some core stuff into separate libraries, consumed as nuget packages by other projects. Those libraries and other standalone projects in separate repos.

Then a "monorepo" for our main product, where individual projects for integrations etc will reference non-nuget libraries directly.

That is, tightly coupled code goes into the monorepo, the rest in separate repos.

Haven't taken the plunge just yet tho, so not sure how well it'll actually work out.