I'm glad I procrastinated. I've been meaning to pick up a SIG556R, and the new model looks like a more or less "Patrol" model of the SIG556R, which should alleviate the purported nose heaviness of the weapon. The option for different barrel lengths is awesome too.
"Like the MCX and MPX, the user can simply swap the barrel and the bolt, and it's ready to accept the appropriate magazine! And speaking of mags: the caliber-swapping variants will all accept AK mags, Stanag mags, and AR mags."
I think the author's probably incorrect or confused here. The multi-caliber model will probably take AR mags, AR mags, and 7.62x39 AR mags. Still neat though.