Hypothetical: What Still Needs Fixing?

[Dionysusigma]

The AR design, is (more or less) 60 years old. Since its initial development, it's been frequently and sometimes nonsensically modified, updated, made from almost every possible material, accessorized, accurized, shortened, chambered in as many different calibers as any hunting rifle line, used in every operational environment this planet has to offer, and is still going strong.

Over that time, included in numerous issues that have been addressed are a standard of gas port size requirements; buffer weight; charging handle (from the original "trigger inside the carry handle" to the comparatively-new AXTS); barrel lining, barrel profile, and total barrel composition; trigger/hammer/disconnector/spring group; sights; ergonomics (i.e. furniture options); and countless others. And all have been, more than with any other system ever in such widespread use, cross-compatible with nearly every variant produced. A person could put a BCM GFH Mod 5 charging handle on a Colt 601 (however blasphemous it might seem).

But what, in your opinion, still needs fixing? What glaring (or mildly annoying) issue bothers you? How could it be changed?

To simplify discussion, let's try to limit the possibilities within the following:
- STANAG magazine compatibility
- Mechanically safe (e.g. no paper-thin chamber walls or skeletonized uppers)
- Remain within the "small arms" definition (nothing crew-served, portable and usable by one person)
- Be fully compatible with the majority of another AR - several push this envelope, from the fully ambidextrous lower of the SR15E3 to super-short PDW systems, but may be included because they can still be "mated" with the other half of the system
- Use materials that currently exist (no Star Wars Durasteel bolts or using antimatter instead of H335!)

Edited to add: This is all made from the assumption that the AR operating system (for lack of a better descriptor) is the pinnacle of firearms development. For the sake of argument, let's maintain that bias. The Sig MCX thread comes to mind...