I've seen some of the amazing weapons on the History Channel. Range-finding grenade launchers that blow up right over the target. Hard to hide from those.
Combustable cases are pretty neat. Don't need an extractor, ejector or an ejection port.
Combustable cases offer the benifits of caseless rounds without the disadvantages (problems that plagued the HK G-11 rifle).
My next concept is a sniper rifle that fires a laser-guided bullet which homes in on an infrared laser (so as not to be visible to the naked eye).