It looks like this will also follow the template of the Spelljammer books, with some player options, setting information, and DM facing content (adventure & creature statblocks).
Looks like no new subclasses based on the description. Nor are there any races listed (what's the new term? ancestry? Species?) so this feels lacking in the character options as well. Maybe that bodes well for the setting materials?
Discover 2 new backgrounds, the Gate Warden & the Planar Philosopher, to build planar characters in the D&D Beyond character builder
Channel 7 otherworldly feats, new intriguing magic spells & more powered by planar energies