Ability to clone only certain parts of a repo. Git has shallow and partial clones, but they don't feel like the right tool for large/mono repos.
Not really.
CVCSs are commonly used for monorepos and large repositories. The most popular FOSS option is Subversion, although it may not be favored by all programmers and users. Perforce is another option, but it is a proprietary system.
Ability to clone only certain parts of a repo. Git has shallow and partial clones, but they don't feel like the right tool for large/mono repos.