pdt,
To quote Clayton Christensen, it is not only unknown, it is unknowable. The huge factors in FCV adoption are:
1) ICE alternative - gasoline prices, regulations making ICE's expensive or not fun to drive, success of alcohol / natural gas / hydrogen ICE alternatives
2) EV alternative - battery prices, battery specific energy, battery rapid recharge / life / price trade off, battery charging infrastructure
3) FCV alternative - fuel cell prices, rare earth element availability / prices, hydrogen infrastructure, low cost conventional fuel reformers (gas, diesel, alcohol, natural gas, etc.)
Any of these factors could change with a major innovation that tips the balance their way, sooner or later. So far, I am not seeing a cheap, high specific energy / power, rapid rechargeable, long life battery come to market, so the door is still wide open for FCV's, especially in cold climates. Toyota, Honda and Hyundai will be offering FCV's in 2012, so start the clock there. Given the high performance capability of such a vehicle, they can certainly surpass the poorer performing hybrids' market penetration.