Probably all true, what you say about magit and so on. Message passing values would be an idea, but with the current situation, when 1 concurrent execution units, a process, finishes its job, how does its "private" potentially modified state get merged back into the main Emacs global state? Lets say the concurrently running process creates some buffers to show, but in the meantime the user has rearranged their windows or split their view, but the concurrent process doesn't know about that, since it was after its creation time. Or maybe the user has meanwhile changed an important Emacs setting.

I think the current solutions for running things in separate threads are only for external tools. I guess to do more, a kind of protocol would need to be invented, that tells a process exactly what parts of the copied global state it may change and when it finishes, only those parts will be merged back into the main process' global state.

Maybe I understood things wrong and things are different than I understood them to be. I am not an Emacs core developer. Just a user, who watched a few videos.

Tramp can be sped up a bit. I remember seeing some blog posts about it. I guess if you need to go via more than 1 hop, it can get slow though.

What is the problem with mono repos?