Mine is a Late 2013 rMBP.
What is everyone seeing in their Consoles?
I see this (and a bunch of other meaningless crap) every time a freeze happens:
kernel[0]: Trying to restart GPU (Intel Iris Pro)...
... along with a hang analysis for the GPU restart. Sometimes it happens once, sometimes twice, three, four, five, ten times... I guess this is why the hangs sometimes take longer: it tries to reboot the Intel Iris Pro GPU, and it fails, so it tries again and again until it succeeds. The system freezes until it succeeds.
Maybe it has something to do with YouTube videos now being GPU accelerated, requiring the discreet GPU to turn on for the video or something, and then once you're done watching the video, to turn off, and this switching is what's causing the problem. This seems to imply a hardware malfunction, which is likely considering that I've never come across a Mac with a discreet Intel GPU that didn't also have a hardware failure related to the GPU.
Also in favor of this being a hardware problem is the fact that Apple is not responding to the issue, and that no software update has been issued to address it for an unusually long time. Well-documented, widespread software issues like this one tend to eventually get solved within the meaningful lifetime of an OS, even if they're never officially acknowledged by Apple.
Apple probably did some tests based on what we reported, realized that a batch of computers they sold are all faulty, did the math, and said: "Yeah guys, you know those new computers we released that can't be repaired at all because they're basically filled with glue? They're all screwed. We messed up the GPU soldering, again. So yeah it's not worth it, we'd need to give everyone new computers because we made them to be unrepairable. We'd lose money, let's just say nothing, the idiots will just buy new computers next year anyway because they'll be thinner and made of GOLD, and then we'll make money instead of losing money. Isn't making money better than losing money? It definitely is. So rose gold it is! Make sure to fill it with glue."