Rick and Jon recorded an album together recently, just voice and keyboards. A logical question would be whether they might do a follow-up, or another tour, or whatever. Jon and Vangelis recorded a few albums together years ago, but supposedly they had a falling out. Those albums were more interesting IMO because Vangelis brought his entire array of keyboards. The Living Tree (Jon and Rick's album) is mostly just voice and piano, with some string and brass patches, and electric rather than acoustic piano, but overall the arrangements are pretty sparse. Maybe ask whether a more adventurous album a la Jon and Vangelis might be in the cards.
There have been rumours of an Anderson-Wakeman-Rabin collaboration. It would be nice to find out about that first-hand as well. Rick Wakeman and Trevor Rabin have both spoken many times of wishing to work together, but it never seems to work out. Seeing as how the one band they have in common is Yes, yet they've never actually played together on a Yes album, an Anderson-Wakeman-Rabin album makes perfect sense. So what's up with that?
It's actually been quite a while since his last solo album. Is there possibly another solo endeavor down the road?
His health is a genuine concern, and cited as the reason for his departure from Yes, or Yes choosing to move on without him, depending on how you interpret the events. He's still not 100% healthy again, and may never be, given that he's pushing 70 now. Does he plan to retire some day, or will he literally continue making music until he cannot any more?
Jon is a very spiritual guy. What does he believe will become of him, his spirit, his energy, when he passes on?