Use the following template for a nicely presented post:
{{Forum post|Write your message here!|~~~~}}
On a side note - is there a listed spell that can transport a character from one campaign setting's material plane to another campaign setting's material plane? The only possible candidate I can think of is the 2nd edition: Worldwalk spell. It can be found on page 67 of Forgotten Realms Adventures.
Heck, as far as I can understand there's a novel where a Kender (think Dragonlance) manages to get into the Realms, so yeah.. Confusing, and I think the writers at Wizards manage to confuse themselves too.
The main rule of Spelljammer is that the influence of gods ends at the crystal sphere. So within Realmspace the gods of Forgotten Realms (including the gods of Maztica, Al-Qadim and Kara-Tur) are in control and in other crystal spheres they are not in control. If the planes change for Forgotten Realms 3e, they can change for all of Realmspace. Each crystal sphere can easily have its own cosmology. This isn't something that WotC have developed, they have pretty much ignored Spelljammer. But they have never said it no longer exists.
Forgotten Realms Campaign Setting actually supports the existance of Spelljammer (and Kara-Tur, Maztica and Al-Qadim). Read the section called The Sea of Night on pages 230-231.
There are some older Forgotten Realms products that also have specific Spelljammer references:
Forgotten Realms Accessory: Gold & Glory mentions Code Helm, Emerald Brotherhood, The Enforcers and The Gauntlet. Four mercenary groups found in Realmspace.
Dungeon Crawl: Undermountain--Stardock is an adventure that starts in the tunnels below Waterdeep and then takes the players through a portal to one of the Tears of Selune called Stardock.
Arcane Age Accessory: Cormanthyr - Empire of the Elves mentions opposition to the Netherese spelljammers by Cormanthyr and the Elven Imperial Navy and also the Elaorman ritual used to create elven crystal spelljamming ships.
Arcane Age Boxed Set: Netheril - Empire of Magic includes information about the Neteril spelljamming ships and spells to permantly seal crystal spheres and create ships that travel at double spelljamming speed.
I'm sure there are other FR products with hidden SJ references in. I suggest you check them all before you make a decision, as excluding Spelljammer would invalidate all the products that mention it.
Check out Beyond the Moons's products page for more information about Forgotten Realms products with SJ references in them.
I believe that the biggest problem beween Forgotten Realms canon and Spelljammer canon is that one of the Forgotten Realms products (I can't recall which at the moment) says that the Rock of Bral is one of the Tears of Selune and this conflicts with the Cloakmaster Cycle novels that put Bral in Spiralspace.