I always thought webOS was really nice and ahead of its time. I assume making phones using this would be difficult without having good driver support from the hardware vendors?
Speaking as someone who has (a bit) worked with Firefox OS, the answer is very much yes. Also, that's only the start of your worries.
Curious what you think the problems are. Drivers are a huge one IMHO (as the parent poster mentioned). From a tech perspective, perhaps the biggest one. The only other tech major tech challenge I see is getting app developer support (basically, what killed Windows Mobile).
Baseband is one, if the other commenter doesn't get back to you.