People seem to conflate a monorepo with having everything else the same as well, just because that's how Google and other BigCos do it. You don't have to.

At some level a monorepo is just a way to stick all your code in one giant directory and manage it all under one VCS repository.

You could still do separate build tools per project, separate vendoring if you really wanted and so on.

However you may find that being able to simply import other first party code by path instead of doing some cross repo dependency process is a massive win.

Edit: apologies, this was meant to be a reply to the top level comment.