Honestly, I would never want to see Paul tour with another artist I liked because no matter how good that other artist was I would never be able to appreciate them knowing Paul was coming on next. I've seen a couple of these double headliner tours and it always happens, one band no matter how good always pales in comparison.
For example, I saw Cheap Trick open for Aerosmith a few years back. Now these are two of my all time fave "live" acts (not necessarily recording) and as much as I love Cheap Trick and as great as they were, Aerosmith completely blew them away. And for a while my perception of them as a live act had changed. I didn't like the way it made me feel about one of my favorite live bands. Another example I saw Tori about 8 years ago with Ben Folds. Never heard of Ben Folds, but he upstaged her in every way. Again, didn't like it.
And as for recording together, I have no desire to hear Paul do any duets again. A collaboration is okay, but it needs to be Paul front and center a la Fireman.
Wait, changed my mind I think a Paul/ Davy Jones concert would be awesome!