Well cant use them inside because the space limitations. And if you use them outside you have a bunch of other problems--too many people going onto rooftops and stuff, and most of the maps probably have unfinished rooftops and courtyards too so Cryptic wouldnt want you flying around on those maps and getting behind walls and stuff.
Not gonna happen until they are ready for it. They aint ready for it.
Shelve the jetpacks, but think about that Risa map...the possibility for KotH, CTF, Assault, Dom, etc, etc, etc...
Might require "invisible walls" for various gameplay types, but some of the new maps have been pretty lush for various things like that...heck, consider the Nimbus stuff and the possibilities there, eh? Heck, even work I-18 into that, hrmmm...fighting through the corridor for a set period of time, to see where the line is moved.
There are a lot of things there...just a case of how they can get a return on the investment from any of it.