Thankfully the differences between a raster and vector screen are not as extreme as you might believe. Both are analog and work with similar signals and use the same types of shadow masks and phosphors. The display part of a CRT shader, from the gun to your eye, should be able to be identical for both.
The signals the displays use aren't too different in nature. There are the video signals, RGB, or just Y for monochrome, for both. Rasters have H-SYNC and V-SYNC ramps whereas vectors have arbitrary x and y signals. You can construct frames with strict timing with sync signals but no such thing exists for the vector displays.
If we want to make things like the Apple II or LaserDisc accurate we will have to deal with the video signals directly anyway, and that should naturally lead to work on the vector games hopefully. To have better phosphor effects, especially with the increase of high-speed displays, MAME will have to switch to a new method of display where black frames are inserted (the persistence models keep the screen from actually becoming completely black). Another change is to make the phosphor effect additive instead of the 'lighten only' method it uses now. This should have the potential to make the vector lines look much more realistic. I've been experimenting with this additive method (for rasters) but there are some aesthetic issues and difficulties that people probably won't like.
I can't work on vector things directly, but I will at least try to port it to BGFX along with my other work, and hopefully other work I do will improve vector games as well.