Funnily enough my first (published) storygame was a coauthored one. Alas, I'm not currently looking to coauthor another (too many projects would murder me).
Coauthoring is generally not looked on too fondly around here, but like pretty much anything writing related, it can work. Then again, in some ways it can just add more points of failure. What if you don't lose motivation but your coauthor does?
As such, my advice is setting expectations early and maintaining clear communications. Working towards some kind of deadline isn't a bad idea either.
The general advice of keeping the scope in check and starting small still applies.
Good luck with it! Ford is a valued member of the community who has shared some good stories in the past. Would be great to see what you two can cook up!