> 1. A good concurrency model.

This is definitely the biggest pain point, especially as people go to expand their use of Emacs (e.g. with Doom, adding more modules and integrations, one has to be careful to lazily evaluate config blocks to avoid loading everything at startup).

Even without such extensive configs, working on a large repo with a slow I/O (e.g. some network mount) with magit will cause large pauses once a command finishes if it has to refresh the magit buffer, or trying to search myriad org agenda files for an ID or text search (e.g. org rifle) will basically lock up emacs.

I do at least look forward to Emacs 28, which iirc is going to get native-comp (although that is already available as an experimental branch perhaps?).