There was one, a few years back, some kind of 5.56 (used M16 mags) on top of a 20mm? grenade launcher with computer programable grenades. As I recall (vaguely) it died because they couldn't make weight (they did get down to 18lbs) and somebody found out that the grenade rounds cost several thousand dollars apiece.
We're willing to spend thousands of dollars apiece for artillery rounds, and even a million+ a pop for cruise missiles, but that much for infantry rifle grenades (even if you could program them to go through the window and THEN explode) was just too much.
I'm not sure, but I think the military no longer does its own development of small arms, they farm it out via "research contracts", and so they get all kinds of things for the money.
At the moment, and for the near term forseeable future, we're not engaging in land combat against the regular military of a nation state. And, while I'm sure there are contingency plans, at the moment there is no valid threat from anyone's organized military (China, and Russia are distant worries right now) facing human wave attacks from a "red horde" looks pretty slim.
The most credible threats on the horizon are not going to be faced with a "new and improved" infantry cartridge /rifle.
So finding something that "works better" than what we're currently using, and at an acceptable cost, has a pretty low priority.
We didn't adopt the .276 Pedersen, arguably a more efficient round, because of the huge investment we had in the .30-06. Whether or not you think the 5.56mm is the right round, we're not going to be replacing that, either, anytime soon, for the very same reasons.
Remember that while research can come up with all kinds of wonder weapons, if they aren't enough better to justify the cost of replacing what we use now, they aren't going to be bought in anything other than small numbers (if that) for testing.
Somewhere I read that the average infantryman's load in WWII was 40lbs, and the average load today is 80lbs. the numbers might be off, but the point is our GIs today are heavily loaded down, and I see lots of pictures of them going into combat with a full ruck load on their backs. Seems to me powered armor like sci-fi "mech suits" might be something we're going to need before long, just to carry what "higher" decides is needed.
That tech (to a military standard of function and reliability) is still a long way off. Drones (flying and ground operating) seems like something cheaper and more achievable. If we go that route, they aren't going to need a new rifle /cartridge, either...