I the past it was very tough for shooters and lovers of the M14 to let go.
This holds true to day with the M4/M16/C7-8, fans will have a tough time letting go.
Newer systems are better, SCAR, HK416, Swiss Arms ect. It will take a while before the fans let go and accept those newer / better weapons.
Rich
HK416 still unproven and with the US no longer interested in them likely to never see wide use. At this point in time it seems the 416 is not the cure all, it was once thought to be.
SCAR also unproven.
Swiss Arms = newer

The SA design (as we have it here) is old baby and outdated by today's standards. The updated versions ie 556 have had some pretty major combat issues that have pretty well ruled them out as well, if they have fixed the bolt issues I haven't heard.
The point isn't that there are better systems available its just that most of these new systems offer minimal improvement over a quality M16FOW example. The world awaits a new innovation that will be as revolutionary as the M16 was back in the 60s. Honestly though where is there room for massive improvement?
Bolt design? not really.
Ergonomics? maybe just the bolt release for lefties.
Weight? nothing drastic without polymers like the G36.
Endurance? hard to say as quality examples like the C7 seem to take a lot of use.
DI action? maybe but how much better and at what cost? again the G36 is nice but they traded the weight savings of the polymer for the weight of the gas system. That said I doubt we'll see another DI rifle in the future.
Imagine if you will the US had accepted the XM8 as is. They would have less modularity then they do with the M16. Its all give and take. The wide variety of options the AR now has make it hard to beat. And despite its flaws in general combat is seems to be about as reliable as needed.
Maybe a bullpup design will be the key who knows. Right now though it seems obvious the M16 is gonna be around for a while.