[0] https://www.legrand.us/wire-and-cable-management/raceway-and...
There is a small triangular void that you fill with a triangular piece of wood [backing strips, that's the phrase I was looking for] or some wedges at intervals in order to support it.
In this age where rare earth magnets are getting cheap, it'd be cool to have wood or coated MDF trim that's secured with magnets and little ferrous iron inserts. Then you just need a stronger magnet (like those passive stud finders) to pop the whole thing off and run more wires.
Of course the next problem is you have a narrow, concealed raceway full of plastic insulation, which is something that rodents like to chew on...
If I try to look for crown molding, I'm seeing a lot of accent light solutions built into plastic molding (you leave a gap for the light to come out from behind the molding). It's... okay. I'd rather have 10g ethernet in my house though.