Originally Posted by skingry
Also, if I could find a big wheel in my size that would hold my 230lbs ass properly... I'd ride it everyday.
Ask and ye shall find...
$300, 250 lbs weight limit.
And to dovetail this all back in to the original topic... I am in agreement that a SS/FG certainly falls into my idea of adventure cycling but then again I believe adventure cycling is more an attitude to a variety of activities than a particular bike design. Is riding around the neighbourhood chasing your friends (Ride-N-Seek) considered adventure cycling? Is offroad cyclotouring adventure cycling? Is road touring adventure cycling? Is cyclo-geocaching adventure cycling? I would have to say all the above are forms of adventure cycling and for each there is probably one or two types of bikes that is optimal for each.
I think it would be hard to create one bike that would be best for all but one bike could be made that is adaptable enough to allow you to engage in all such activities. I think the OP is on the right track with the dropouts. Another idea would be to use fully replacable dropouts such that a SS/FG conversion could be done relatively quickly and easily.
I would also look into making sure that the derailleurs and brakes can match up and work with both MTB-style shifters/levers as well as road shifters/levers alike so that you can swap out control types and bars easier. Perhaps look at using the new range of flatbar controls for your flatbar. And if you're going to do the S&S thing then of course you'll want to have quick-disconnects for the control cables too so this should help facilitate swapping between drop and striaght/riser bars.
Basically what you want is to design and spec the bike so that you have options for quickly interchanging and modifying the bike from a MTB to a touring/cyclocross style bike. I suspect your geometry will most likely be close to that of cyclocross frame.