A bit late to the party here, but thought I'd respond anyway
The only one of these I could (potentially) see happening is space stations. The other ones would really, really mess with the AI - that's the main problem with having more interesting environments. The ways of dealing with them are very hard for the AI to handle, and so it would just end up being a way to cheese the AI rather than bring variety. Well, I suppose that's variety in some sense, but not good variety.
Welcome to the party
I am more concerned with the ability to differentiate battle types based upon overworld map position honestly. I have plans for that
But yeah I understand A.I is tricky business for some things, just certainly not everything.
For instance as far as nebulae are concerned.. I think it is perfectly acceptable to use something like that to have an advantage against the A.I in actual combat, but the A.I response to it would rather be at the campaign level than on the battlefield where it there would have to be a separate AI written to account for it. Larger, slower fleets simply would avoid those areas and be unlikely to chase you into one. Pirate raiders would favor them and the player then has to decide whether to engage unfavorably or not if they have a slow fleet. The balancing part would be how often do you find them and making sure you cant use one to game an entire faction or something like that.
Writing A.I for those things on the campaign level wouldn't be nearly so hard because there is less to account for.
For asteroid fields, same response campaign level, but simply add asteroids to the list of pd targets with priority depending on the size of the asteroid (a.k.a how much damage will it do if it hits me?) and make asteroids less common or not exist at all outside fields.
At the end of the day, I think it is way better than the same thing every time. Or even worse, random battlefield objectives or hazards such as the current set up. Random is almost never good in that kind of situation because it either has to be trivial enough to be meaningless (as it currently is) or can be a frustrating experience for players if it makes too much of an impact and is completely beyond their control.