I agree that small sectors would make the small size of the nebula somewhat lacking. I suppose that's just something people would have to deal with if they decide that small sector size is what they want. I think a 5k sector size would be sufficient, which could give a 3k (500m shallow x2, 750m deep x2, 500m dark) to 4k (625m shallow x2, 1k deep x2, 750m dark) total nebula size. Again, it's mostly what is feasible to implement with what I have in mind.Yay my station was used
As for the idea itself, I do like it, but I see some problems with it being only one sector. For example, if the sectors are small then there would be a very small sphere of nebula which even medium ships might stretch all the way across.
Also, I have to agree that it would be a really good new type of system that could spawn, like wormhole-systems do currently, but could also spawn in the void (maybe??). It should not spawn stations in and any stations built inside should be completely hidden regardless if they're discovered or not, necessitating actual scouting missions inside and faction communication to assault a base inside. However maybe increased asteroid spawning inside the Shallow and Deep zones? It would make these zones highly desirable faction bases and nesessitate the defense of said zones.
I acknowledge the idea of making them system sized, but I think that would somewhat reduce their greater tactical advantages and overall fun. I totally agree that stations shouldn't spawn inside them, but instead perhaps small remenants of lost civilisations or ancient explorers. I hesitate to call the spawning of rocky objects within nebula 'asteroids', because they are not strictly so. Fistly they are always immobile, unlike asteroids. And they could also have some unique blocks such as plant life, though they would still possess ore.