It is a fascinating challenge and, at some point, guinness may have to define supported and unsupported attempts. Alan bate's record is astonishing, and very impressive, but he's done something different to vin cox (and mark beaumont before etc.).
I'd guess the next great target for unsupported riders in the 150 day barrier?
In terms of supported attempts, beyond the phenomenal fitness required, it becomes more and more a question of financing. If someone can raise the capital for a 3-5 person RAAM style support team, then their chances of success will be improved.
Anyway, back on topic, I would love to go to the start, looks unlikely though as it's my other half's birthday.
And if you do the ride in 2014 rich, I am sure we'll all be supporting you every mile, and be insanely jealous!