Does "
honey sriracha aioli" sound better?
Back in the day, while we did do a little traveling from setting to setting, our Spelljammer adventures generally all took place in space itself, whether it was fighting other ships, carousing at the Rock of Braal, or seeking out the eponymous Spelljammer itself. It very much has its own flavor and feel. But of course, that probably varied from gaming group to gaming group.
I do think that the connective part is important. As I've said before, the settings of Spelljammer or Planescape need places for people to go. And as Wizards adds more and more settings, they're going to want to avoid the market-fracturing of 2e and establishing strong ties between them all is one way to try to do that.
I view both Planescape and Spelljammers as metasettings, they aren't settings in their own right, they merely connect settings, the means to move between them.
The Planes and Sigil are the actual setting in Planescape, with is really just the way they all connect, as well as adding a theme of philosophical exploration to all of them. The settings are Aborea, Mount Celestia, Abyss, Hell, Hades, Archeron, Fire, etc..., each a large setting in it's own right, with Sigil connecting them all to each other and the material plane settings.
Spelljammers does the same, but excludes planar settings originally, but adds in it's own material plane settings.
So all "Planesjammer" would do is create a connection in Spelljammers to the Planes, but it's would still predominately be Spelljammers, but with a planar element, but still leave a Planescape/Manual of the Planes book open for deeper exploration of the Planes, and the impact of philosophies on the settings.
So "Planesjammer" would be 75% to 90% Spelljammers and 25% to 10% Planescape.
I also think the mirror Planes will fall more into Spelljammers pervue then Planescapes, as they mirror Planes are closer in nature to the material plane, with major twists then they are to Elemental or Outer Planes.
MtG side Alara and Kaldheim also are more metasettings then settings.
Forgotten Realms is a setting with elements of being a metasetting (if Meta setting vs setting was a scale Planescape & Spelljammers at 9 metasettings and Greyhawk & Dragonlance a 1 settings, FR would would be 3 or 4).