I actually thought about it once on a regional basis, as a 10-15 watt tx puts out a solid signal to about 600 miles. You would have to run diff. frequencies for all but the furthest apart due to HF propagation, otherwise you'd have a bunch of overlapping signals in parts of the country, which would make a fine racket, but would likely be unlistenable.
Imagine the fun of doing it all on one frequency in SSB in the same manner, from different spots, all in sync? Sweet Jesus, that pile of noise would wake the dead!