There's also mutual deployments which suck really bad i.e. deployment A needs to go out with deployment B; but if you haven't set up your CI with that facility

There's also mutual deployments which suck really bad i.e. deployment A needs to go out with deployment B; but if you haven't set up your CI with that facility (and, let's face it, the easiest way to set up a CI with multi-repos is on a per-repo basis), it can get really hairy.