i hate monorepos but for Go the trial of constantly updating the go.mod if you have two repos that are interdependent or one dependent on the other it's a lot of rigmerole 

compared to just keeping it together

once one part becomes stable you can push it out and any further patches later on will be small usually, and not so onerous as every time you are changing each one in parallel 

having to make sure everyone who is working on one side knows what is happening on the other side

until a cluster of libraries are tested, stable, and the client is using them adequately, monorepo is the way TM