Say, the gas giant dimensions will be accessible in the "Planet Select" but instead of allowing you to land you will be required to build some kind of geostationary station at Y=128. You'll be able to see the clouds rushing and thunderstorms under your base and all fancy stuff you'd expect from a gas giant.
It's an interesting idea. It makes me think of how Jupiter is seen from Io in the game Battlezone:
Although, it has been
really exaggerated in Battlezone. It's more like Jupiter seen from Metis, and that moon actually lies inside of Jupiter's synchronous orbit (although, a notable thing is Jupiter actually has multiple synchronous orbit radii due to its various belts rotate in different speeds).
Anyhow, distance would still be pretty long, so maybe if one fell off the station, you'd alternatively get teleported into Jupiter's dimension? Regardless, a transition technique could be utilized akin to how the player starts to see Earth/Minecraftia during late ascent.
If you -- by accident -- fall off your base... you know the rest of the story.
I can right away draw the analog of falling off the ledge in SkyBlock Survival. But instead of getting the announcement "
player x fell out of the world", it could instead be something humorous like "
player x tried to be the first person to step on Jupiter".