I've had the opportunity to handle the 416, 417, MR556 and MR762 over the past few years' SHOT Shows. I really don't care about the proprietary parts issue. I own several different firearms and none of them are duplicates, so parts commonality with other guns in my inventory is not a concern of mine.
What does concern me is the weight of these rifles and their price point. The "Mister 556" feels like it weighs as much as an M1A, and the 762 is even beefier. To top it all off, I think the pistol grip and buttstock are absolutely hideous. I think they had a much better looking rifle with the earlier 416s. I've heard rumors that they will come in at around $3k, and that is just too much coin for any semi-auto in basic factory trim. To me, these rifles are just updated ARs, which makes me more drawn to guns like the SIG 556 Classic & SWAT, the new generation AUGs, and the FNs (although they can keep their Flat Dark Bronze).
All in all, too much money for a gun that has a lot of qualities that I dislike. Nonetheless, I'll be amused when people are lined up begging for the chance to toss $3k into the basic rifle. This coming from a guy who likes HK products...
B9