I have something perhaps quite futuristic in mind: A combination of a Rebreather and a device similar to a fish's gill. Basically so that the stuff we carry underwater is as small as possible, and using all the oxygen available underwater (some oxygen from a small cylinder perhaps, some from our outgoing breathes and some from the water itself).
The idea for the "fish-gills" I got from the first new Star Wars movie. So yes, maybe this idea is too Scyfy-ish.
http://www.gmanetwork.com/news/scit...eathing-mask-concept-mimics-fish-gills/story/
Anyway, for me the best thing about diving is the freedom underwater, freedom of movement especially. The thing I never liked about Scuba Diving was the huge BCD we have to carry around, including the tank and all the other technical equipment (that's why I prefer Freediving now - but that has other, obvious liminations like bottom time).
Maybe someone with technical expertise can help out here and say why this is rather impossible... but if it works some day it would be quite cool.