What do you think, is it possible to make a Laniakea supercluster cmod model?
Can it be done?
Yes. You "just" need a catalog of all 100,000 galaxies and then translate them into Celestia's xyz coordinates. (I don't plan to do it. I'm in the middle of too many other things already.)
+ Do you know any add-on which shows the names of the Milky Way arms?
One step of the Addon that I created of Orion's Arm wormholes projects the NASA/Spitzer galaxy artwork onto the plane of the Milky Way.
Install it, run its script, type an ESC while that map is being shown and then you can change your viewpoint however you want.http://www.classe.cornell.edu/~seb/celestia/orions_arm/index.html#4.0
+ Any star collection add-ons containing stars in the observational shadow of the Milky Way?
No. They'd be entirely imaginary, of course, although one could (in principle, at least) use montecarlo techniques to generate stars with appropriate spatial and stellar type distributions. Cham sometimes does that kind of thing.