I just checked, procedural nebulae are set to display. There seems to be no problems generating supernova remnants or planetary nebulae. The only way to get diffuse nebulae to show is to restart SE and hope that it works (they are displayed about 1 out of 5 restarts).
It seems like this game really loves to leak memory, at least on my system (don't know that it could really be related to hardware though). I'd really love to be able to cruise around for more than 20 minutes. It seems like very little gets cleared away in VRAM and RAM when you travel from system to system. Currently, it appears memory usage does not decline as long as the process is running.
Maybe pair coordinates to your pointers for data related to celestial bodies, then destroy them based on distance from the player?
All that aside, fantastic work. This really is a mind blowing program.
Pertinent system specs for reference:
EVGA 770GTX 4GB 8GB DDR3 i5 4570k
Thank you for taking this project on, by the way. Your outlook for the future of SE is really impressive.