I'd happily see another OAV or feature film of the SAC franchise, but I'm kinda reluctant to wish for more in case the writers begin to run out of ideas. Both seasons were awesome and SSS was good too but I'd rather they left it there than 'jump the shark'.
SSS, for all its Tachikoma action and whatnot, felt like it was relying heavily on paying tribute to the series and movies. Don't get me wrong, I really enjoyed it, but it didn't really push the envelope in terms of themes and ideas. Unless Kamiyama and Oshii come up with something really special, I'd say the franchise has reached its peak already.