Just throwing in my preference, since I can't claim to understand "the market".
A book on blogging would be disastrous. I'd hate to see "the blog delusion" perpetuated further than it already is
You know -- that idea that blogs are some magical money making machine, and all you have to do is post valuable content at formulaic intervals and the blog genie will visit you every month and give you a check out of thin air.
I could potentially see a time management book being interesting. Honestly, GTD left a sour taste in my mouth and I didn't find it useful at all. You'd probably appreciate this Steve -- a simple change in my diet did more to my "time management" than any manilla folder ever could. There's a lot of room for improvement in the time management "field" -- perhaps a holistic method that gets into the science, health and psychology of mental energy levels, focus, etc.