The world has pretty much shaken things down to either the NATO 5.56mm, or the ex-soviet 7.62mm round. Usually the choice for most countries is cost and availability. Most countries that use 5.56mm now have weapons that use M16-type magazines, rather than their own unique types. This is a benefit because a lot of people are now working on their own ideas of how to improve these magazines. And we have millions of American civilians participating in the testing and debugging process, which is also a benefit. For civilian use, and for some special ops use, the .308 is still the best choice. That's why besides the .223 we still issue a variety of .308 rifles, including AR-10s and SR-25's as well as Remington Model 700s.
Strangely the FN-FAL 20 round magazine is almost indestructable. You can stand on an empty one without damaging it. Pre-ban you could but them all day for $7 a piece. Looking at the SCAR it appears to me that it may use the FAL magazine. (That would make sense, both guns are FN designs. Why redesign what wasn't broken.) It's odd that 40 years into it's time as the rifle of the worlds most powerful military the AR-15 magazine is still an issue.
One of the main problems with the FN was that it didn't have any provision for mounting optics. Another approach to upgrading the FN design has been taken by DSArms who has many variations, including "flat top" designs that make mounting scopes a lot easier. Most go for about $1800. 
Armalite makes AR-10s, they are the first of the reproduction makers to re-introduce the AR-10. They have both flat top and iron site/ carrying handle models. My favorite of theirs is their clone of the original AR-10, which was only used by Portugal and their clients in Africa - Mozambique and Angola. It has the charging handle inside the carrying handle, another idea that the Army did away with when productizing the design. (Along with reducing it to varmint caliber.)
This is close to the way Eugene Stoner originally designed the gun.
DMPS Panther Arms is the other viable source for civilian .308 caliber AR-10s.
Happy holidays! Stay armed! Stay safe!
trangely the FN-FAL 20 round magazine is almost indestructable. You can stand on an empty one without damaging it. Pre-ban you could but them all day for $7 a piece. I just got a bunch of mags from J&G for $14 each. Not quite down to pre-ban levels but still not bad for a battle-tested magazine that, as you said, is practically indestructible.
One of the main problems with the FN was that it didn't have any provision for mounting optics.
Well, neither did the M-16. That changed with the advent of the flat-topped models. So if you have an old AR with the carry handle you need a new gun to put optics on it.
On my FAL I just put one of these on it:
...and now for an investment of about $30 my FAL has a place to mount advanced optics.
The AK-series is a wonderfully reliable design but the accuracy sucks. This is great for the illiterate soldiers of many non-industrialized countries that are expected to take part in a human wave. Not so good for taking that deer at 100 yards.
The AR-series is a wonderfully accurate design but it's rather delicate and really needs the support of an armorer and a parts department to be of serious use. This is great if you're in a rifle company with the US Army. Less so if it's just you out in the backwoods.
The FNs are good out to at least 400 yards or so and while not as rugged as the AKs, require almost no maintenance to keep them shooting.