I think your valuation of SD over the next 1,2,...20 years is a pointless. I doesn't take into account the fact of SD's competition. It's simply being out out competed. There are more and more sites popping up with better features, lower house odds and more invested developers. (They're probably not btc millionaires, so they're actually interested in turning their site into something profitable)

SD is having it's cake cut slice by slice while it waits to be out performed by all these alternative sites. It will only survive a year if it acts now whilst it still is largely in the bitcoin community public eye. Otherwise this user base will slowly dwindle and diversify into all the other sites leaving SD a husk of a once potential filled 'business'.