Has anyone noticed SRAM Dual Drive drivetrains with index shifters (road STI and mtb triggers) for both the internal hub and the rear derailleur? Is there anything special about these shifters? The Dahon shifters looks like standard Ultegra brifters. The Trek has SRAM trigger shifters. Can one simply switch the standard SRAM DD single sided shifter with a standard Ultegra brifter?