I think integrating the two would be possible, since they seem to have the same artistic style, mechanics, and probably share many scenery items, the question really would be will Frontier do it or not. It could either be really good for planet zoo, since they'll likely get a lot of sales from the supporters of Planet Coaster, but it could also make the game look like just an expansion of Planet Coaster instead of its own entity. I really hope they integrate the two, making a busch gardens/sea world type park would be awesome!
I also think it could help make the simulation aspect more realistic. Maybe they could introduce better financial or management simulation by having an online server where parks from both games (or parks with features from both games) compete for business and visitors. That would be the ultimate combination of the games in my opinion.