Historical AU could be anything. Stargate SG1 is good inspiration for that actually because they explore a new historical world most episodes. There are so many settings. However, this is me we’re talking about so of course the first thing that comes to mind is Regency. I know it’s cliche and probably not true to life but I seriously don’t care. I will never get tired of deb balls, and dance cards, and “may I have this dance” and arranged marriages.
There’s walks in the park as they court with chaperones and slow discovery of one another. There’s scheming for titles and scandals and estates in the country and townhouses and horses and I don’t know just it’s a fun genre. Probably not historically accurate but I care more about enjoyment than accuracy to be honest *hides in box of shame*
Hmm my thinking about Future AU was basically it was similar to sci-fi AU because of the ‘futuristic’ technology. I mean if we think about how far our technology has come in the past 100 years, it could be possibly to theorize in another 100 years we’ll have spaceships capable of travel within our solar system at the very least. However, I started googling as I was trying to write this answer and I was confusing myself, and now my googling has confused me even further so now I don’t even know what Future AU is.
I mean is Future AU just anything post-canon? Like the show ends, if the pick it up then and continue wouldn’t that be a future AU? Like I said I’m very confused now. So I think my answer is going to be Historical AU because I know for definite what that one is.