> Or you can put code in different package and guard internal package cohesiveness and coupling a bit and use well defined interfaces to call a functions through.

While I do think actual microservices are over-kill. I don't think I've seen code anywhere that survives multiple years where somebody doesn't use internal state of another package. Like if you don't force people to use a hard barrier (i.e. HTTP) then there's going to be workarounds.