Again I am saying Hasbro's plans are an universal d20 system for all the genres, sword & sorcery, superheroes, urban fantasy/gothic-punk horror, or space opera, but this needs time and a lot of playtesting. Not only a d20 system for the TTRPGs, but also for the videogames adaptation, the future of this business. I would bet they want to use Spelljammer to create a new videogame franchise like "Mass Effect".
* I suggest to add Spelljammer the monsters and races from Gamma World and d20 Future(Star Frontiers+Alternity).
The really really large Spelljammer monsters were already ridiculously powerful and big, but back then 2e never had Challege Ratings just XP values for monsters. And I don't think it was ever given at what level a party could ever stand a chance at fighting a Beholder Tyrant Ship, which had the ability to magnify the Eye Rays of Beholders 30+ beholders and their Hive Mother into some very powerful attacks.With a giant crossbow or a catapult from a Spelljammer your PCs could kill giants, a dinosaur or another kaiju monster. How would be the XPs reward when it is easier with "extra help"?