It's not uncommon to split front end and back end logic into modules. I've seen lots of projects where the business logic is even shared between a suite of app

It's not uncommon to split front end and back end logic into modules. I've seen lots of projects where the business logic is even shared between a suite of applications. But it's very unusual to split it over an RPC/IPC boundary - it's usually just linked in. Xi had specific design goals of allowing multiple independently developed front ends. There are use-cases for this type of development but it's largely not worth the effort (YAGNI). The typical application architecture is going to depend on your use-cases. I.e a db app is going structured different from a game or a CAD program.