Some really exciting stuff coming up in Metals. https://github.com/kasiaMarek has been doing a killer job and one of the things she's worked on is multi-root support meaning that you can have a project with multiple builds at various levels contained in your root and choose to "add" them to workspace. In the video you can see a simple example of a frontend and backend independent of each other and correctly reflecting the targets when I jumped between them.

https://github.com/scalameta/metals/pull/5033