Just migrated our codebase to use a monorepo maintained with lerna: github.com/AztecProtocol/AZTEC
And we absolutely love it ❤️
There are of course some trade-offs, such as decreased efficiency in CI/ CD, but we're happy to cope with that at the time being.
We're building a privacy protocol on Ethereum, so keep an eye on Twitter if you're into that: twitter.com/AztecProtocol