The crew system is rather nice. But, crewmembers can be annoying and out-of-place sometimes. Like when your security detail starts occupying your crafting room so you can't use a table or when your mechanic wants to hang out in the greenhouse. My idea is that you can edit a crewmember's pathfinding by setting rooms as restricted, as waypoints or as rooms where he can stay and interact. This would prevent crewmembers from running through rooms you don't want them to, and wouldn't tie them to their place of work (so they could go to recreational facilities). It's probably not the best way, but something like this would be great. Also, separate the crew call button from the interact button and make crewmembers callable from the S.A.I.L.
Doesn't seem too hard to hack something crude, like just a magnet that attracts crew. The bit about one for each kind, mentioned on the post quoted by @IxFa is a bit more tedious to do, but not quite hard, programwise. A complete system, like suggested by @samuel9900 with way pointing, restricted rooms, etc, would be a good thing to program, challenging and not tedious. Maybe I can include it in a mod suite I'm working on. Or later, as an addon to said suite. Added it to mod ideas list, no promises, though. If someone wants to do it and do not know where to start, I can point some directions on how to do the scripting.
That is not as precise as I suggested here. Crew magnets work, but if the room is too far away from other places where the crewman should be able to go, he's screwed.