The queue and test system Uber and Google use for their monorepos essentially do both of those. The restructuring you mention was to use a build system such as Bazel or Buck universally.
1) Two changes which don’t effect intersecting parts of the repo are landed separately. Similar to having infinite separate repos.
2) Only the tests that your code effects are run.
This is all possible because Bazel let’s you look at a commit and determine with certainty which test needs to run a and which targets are effected.
That is good to hear, but I'm interested in finding the patterns that makes this feasible without a build tool designed for massively parallel building, testing, and integration of a single codebase. A lot of the historic reasons for Google's build system come down to "we just like the monorepo but it needs complex tooling to work".
For a complex project you need complex tooling. A mono-repo and a multi-repo system have different needs, but both need complex tooling to work. Neither is inherently better than the other, there are pros and cons. Sometimes those are compelling (which is why a few projects at google are not part of the mono-repo)
For me I prefer the pros and cons of multi-repo. However sometimes I wish I could do the large cross project refactoring that a mono-repo would make easy.
1) Two changes which don’t effect intersecting parts of the repo are landed separately. Similar to having infinite separate repos.
2) Only the tests that your code effects are run.
This is all possible because Bazel let’s you look at a commit and determine with certainty which test needs to run a and which targets are effected.