If you use a rear deraillor to keep the chain on the cog you could still run a double or even triple crankset and front Deraillor, I was kind of thinking of doing this for a snow and slush winter hybrid bike, but I just hosed the works out with wd 40 pro and blew them out with compressed air every 2-3 rides and it all worked great for any conditions I was willing to ride out into.

Bottom line the benefit does not warrant the expense probably......now if you had a frame that the RD mounting area had been chopped off in some accident or a brutal single speed conversion it might start to make more sense maybe.

Bill