I understand the appeal for off road and commuting machines, and possibly touring (but unlikely due to LOW gearing desired for loaded touring). Fast road bikes? Unless you lived in a pancake flat area, I don't think it makes any sense. You're going to lose either high or low end gearing. I guess if you wanted to go for this new 10-50 SRAM Eagle business (which I guess they will be release a road shifter for at some point), you could have a pretty full range, but you'll get large jumps in gearing not generally suited for fast road riding where you try to keep your cadence in a tighter range. I really enjoy the gearing on an 11-25 11 speed cassette myself.

But hey, I've been wrong before. People used to (and sometimes still) say "What's the fascination with doubles? A triple makes so much more sense!"

EDIT: Reading posts just above again and yes, 1x would make sense for most triahtlons and crits.