They are interesting because of their size, but they have a high Fs and low excursion - not qualities one looks for in a subwoofer. They really should be considered pro sound drivers because of these qualities. Now, an extremely large horn enclosure would be interesting. 
JP
Not to be the contrarian here but that is an arguement perpetuated by low efficiency driver manufacturers and people that have never heard hi-e woofers properly implemented. Huge x-max's and mioving boatlods of air only contributes to slow and sloppy sounding bass.
Deadfish, Willie and I all use vintage 15" drivers (we all have 15" Altecs and I also use 15" Goodmans)(oh, Mark just picked up some vintage 15" EV's). The sound of these drivers is extremely deep (think 25 Hz in room), rock solid and lightning fast......and yes, the pictures on the walls visalby shake and the rest of the house rattles when you crank it.
When it comes to comparing the EV's to pro sound drivvers, there are significant differences between the two. Pro sound drivers use a different suspension, heavier cone and have larger motor gaps due to their need for high SPL's. The only way to get the efficiency out of the EV's is the small motor gaps and light cones.
Honestly, if I were looking for a sub, the 30" EV's would right near the top of my list. I'd have to make sure the cones were still (extremely) stiff so they didn't physically distort under load but they will make somebody one heck of a sub.
