Imaginative play-well that was useless
Or with trying to combine elements of it with current interests.
I suppose that's true.
^ Personally, I used to pretend to be someone's pet a lot, and one time I imagined being stuck in a zoo that aliens went to in order to watch humans, and I spent time creating an escape plan.
As for playing house, I was usually either the dad or the family dog.
I liked dressing up, because whenever I did I would pretend to be someone else for a bit.
The imaginary countries went dormant for years. But then I joined a science fiction club in college. It turned out that most of the members were also into combat simulation board games - war games that simulate historic battles (this was the pre Xbox pre personal computer Seventies). Then elements of the fantasy countries came out of the wood work. Got turned onto naval warfare of WWII. Ended up designing my detailed naval wargame. Then one day I got sickened by it. Wondered why the game was so damned addicting. I realized that the game involved lots of.....penetration imagery. Shells penetrating the armor of warships, and EXPLODING inside the hulls. Realized that I was addicted to it because I wasn't getting enough...you get the drift. So I dropped the wargame, and took up social dancing. Started dating more. Meet someone am still involved with. And social dancing sparked my interest in music. Became a party deejay for ten years.
But the game (the tables, the hexsheet, the markers representing ships, the various kinds of cool dice) are all still in a box in my closet. Still break it out sometimes.
So fantasy, and special interests (aspie, or otherwise) come and go, but even when they go than can live on and merge with other interests, and split and joint parts of other interests.
My daughter has quite an elaborate line up for how her toys are placed around the living room. She doesn't actually use them much once a new toy has been introduced, but god forbid I move one, I would be breaking apart horse families! She does have them talk to each other sometimes, but I think it is mostly reliving what she saw on a cartoon or working out how she thinks they relate to each other. Or she does very concrete things like placing toy food next to each animal, but she doesn't do the pretending to feed actions that other kids do. It's just matching the correct food to what the animal eats.
When I was little I used to have my stuffed animals "go to school." I wrote out composition books filled with how to schedule their classes and what they had to learn. Sort of pretend play, but in a really autistic way.