This looks to have an aluminum upper receiver, so it probably won't have the same wandering zero issues as the G36. Gotta love the German government though. How many times has HK dicked them over, now? And they don't look for rifles from anyone else.
Does the bottom of the magwell have the same angle as that on AR-15s, or is it somewhat more horizontal?
I'd bet that this works the same as the SCAR, in that rifles with any barrel length get the same length of handguard, whereas the longer-barreled 416s get a somewhat longer (bulky as shit) handguard. Do different 416s have different lengths of pistons, for that matter?
Relatedly, here we have another modern rifle with ease of modification prioritized over getting the off hand far forward on the handguard. Honestly, how useful is it really to easily change barrel lengths in a military context? Will soldiers be swapping out barrels for every mission, based on what they think they're going to be doing? How much of a pain in the ass would that be for logistics?