I think the next theme may be reality modification. The plot context will probably involve the concept of "dreams." The planet's dream vs. Lavos' dream. The two dreams conflict, and Lavos tries to subjugate the planet to its will in a last ditch effort to impose its spirt on the planet (kinda like a cosmic demonic possession). So the planet must reach out to a team of plucky hero's to enter into its dream to stop the Lavos nightmare (it can't be Crono and the gang because this would all happen during the final fight with Lavos).
Personally I think this would make a great Wii game, with being able to change your environment in all different ways, and since dreams can take on whatever aspects are necessary, they can go to different times or dimensions. Even old locations can be revisited: Ioka village, El Nido, Zeal, etc. and even the old cast can make an appearnce as personification of the planets concisenesses (I think thats what the Crono, Marle, Lucca children were in Chrono Cross). Not to mention an actual appearance of Gran (Masa), Leon (Mune), and Doreen. Though the Planet's dream all outstanding questions can be answered, plus it would make an awesome rounding out of the Chrono series.
