The definition of 'wide audience' is a matter of perspective. MW/SW pirates have the potential to reach far greater audiences than the average FM pirate, simply from a signal footprint aspect. Receiver availability or signal quality are other concerns, but I'm still in awe of the fact that 100 watts can cover a continent on SW, whereas at 100 MHz and a good location, your generally limited to a dozen or so miles.
It is likely in the future that we will play on 1720, but for reasons already pointed out, its a tough cookie to crack, the footprint of the antenna system is the biggest hurdle I see. A 300' circle is hard to fit into the average suburban lot, and low dipoles at those frequencies don't work that great either.
Part of me thinks, at least from a professional aspect, the MW will continue to decline, probably starting with some of the rimshot stations with complicated directional arrays that either cost to much to maintain, or don't generate enough revenue to subsidize the land taxes and power they consume, to say nothing of licensing and staffing costs. This may be one of the silver linings of the AM translator debacle; if the FCC decides that AM's with translators can let the AM plant go dark and maintain the FM signal. It would lead to a new cry for FM spectrum, but may provide a new means for some of these struggling stations to stay afloat.
There is also the matter that FM doesn't seem to have the appeal it once did either. The number of nights I gave out a phone number on a relatively high powered FM pirate and never got calls told me a lot. I'm sure its a different story for ethnic stations that have a built in audience to support it, but the average joe is just pushing buttons, or listening to itunes.
I have a feeling there are more people listening to shortwave than any of us would guess based on some of the email I've received over the years. You never know whose out there, and that's what makes it fun.
Time will tell,
+RH