One BIG drawback is spelled R-F-I.

Putting these high frequency signals over unshielded powerlines will play havoc with other uses of the radio spectrum. Shortwave, public safety, and amateur communications could be rendered just about impossible!

Lots more info on why BPL should never have gotten off the drawing boards:
http://www.arrl.org/tis/info/HTML/plc/

Unfortunately, now that MBAs are running the FCC instead of engineers, crap like this gets approved as a gift to the corporate interests that grease the wheels in Washington... [Linked Image]