It would make more sense for me to develop Windows 8 apps, if it were a PhoneGap target. I've spend a good part of the last ten years developing desktop LOB apps.
It would be like I was in the cup making business, but my cups could only be used to contain peanut butter and jelly flavored vodka. The stuff exists, and it is pleasing to the senses, but it will never represent a large portion of the beverages people consume.
Your last point is purely speculative. It's also a weak argument. Windows 8 is currently at the beginning of it's marketplace adoption cycle and therefore doesn't match the current levels of usage of more established general purpose operating systems (which have been in market much longer). Asserting that this alone means it will never be successful is illogical. Even Spock would question this.