Open bolt is generally more suitable for sustained fire as it doesn't build up heat as quickly and is less susceptible to cook-off, hence its use in MG's (except, most notably for the M2).
LWRC had an entry that fired from closed bolt on semi and open on auto.
As for the IAR? It's been a longstanding project of Gunner Ebby to return to a BAR/RPK type weapon, to address the following deficiencies of the SAW:
*Only accurate from a prone position, and awkward to fire offhand or from a kneeling position
*Increased weight leaves the SAW gunner behind in an assault
*Though it uses 5.56, 5.56 link is still a separate ammo source, and SAW's have mixed reliability with the magwell as they age
*In a 1st/2nd block environment, the SAW is a poor weapon for a discretionary battlefield
I heard secondhand that in a field trial, a HBAR M16 produced twice the hit probability of a SAW. And I believe the original intent was to use a large-capacity mag like the Beta-C (or the large capacity mags used for the RPK), but after that proved to be unreliable, it was dropped. I wouldn't be suprised to see a larger capacity 5.56 mag in development.
As it stands, the SAW's are to be kept around in the platoon TO&E to be reissued if a need arises (say, in Afghanistan's rural battlefield).
