Assuming there's much of a resemblance 60+ years in the future.
That's not really that far. That's like looking at back to the 1960s and looking at how they saw the 201X being... Still waiting on my nuclear powered flying car.....Or my robot butler... or for tickets to the moon to go on sale.... Or just about everything the people of 1950's America predicted.
Caseless ammo has been tried before. Heckler and Koch spent millions on the G11 weapon platform and it's caseless ammo system before finally pulling the plug on the weapon. Some of the problems they encountered were:
Humidity affecting the ammo (making to 'wet' to fire, or too 'dry' and causing a cook off of the entire magazine)
Heat problems. (ammo gets too hot and cooks off)
Moisture problems (ammo absorbs too much water, doesn't fire)
Contamination of the propellant by foreign matter. (AKA, dirt. Caused jamming of the firing and loading mechanics)
And lastly, shelf life. If the ammo was stored too long, it became brittle and jammed the weapon.
Sure, 'advances in the next 60 years' may solve some of these issues, but the old adage of "It's the FUTURE!!!" isn't an answer, as the past as always had fantastic views of the "future"... and they are almost always wildly way, waay off...