Look, if you're not an expert on these issues, you're not adding to the discussion by throwing out uniformed opinion.
While I don't know how qualified you may be, and what your education or work experience in this field is, flaming someone else without knowing their background is uncalled for.
(a) The fact that you have slow internet at your house does not change the fact that there are OTHER usage scenarios that can utilize higher bandwidth. One set set of these is public situations (for example conferences, workplaces) where base stations try to connect to every device as fast as possible, and where high internet bandwidth has been arranged.
I don't disagree, however, how many iPhone users (who don't even know what version of iOS is on their phone unless a genius tells them) will benefit from 802.11ac? ac is backwards compatible with n, meaning that you don't need an ac chip in order to connect to a network with ac, so we're in the clear there.
I agree with your point about bandwidth constraints for "conferences, workplaces" but again, where do we see iPhone 6's being used as routers for these scenarios? I'm not saying 802.11ac is useless in totality, but the user experience from having n -> ac in their iPhone won't be noticeable, if at all, different (after all, this topic is about ac in the iPhone, not about the ac standard in general)
(b) Adding to (a) there are features in 802.11ac that further improve the conference type situation by allowing multiple devices to communicate simultaneously with a single base station. These features (MU-MIMO) may or may not be part of the new iPhones, we don't know yet. (Broadcom announced some months ago that they will have an MU-MIMO phone chipset ready in a few months, but gave no more details. It is not inconceivable that Apple has arranged to be the first purchaser of that chipset.)
So as you stated yourself, MU-MIMO isn't actually ac itself, but a feature that Broadcom could incorporate. It's likely not even going to be incorporated into the "first draft" of ac from what I've read, and comes with plenty of caveats.
(c) Adding to (b) there are features in 802.11ac (in particular beam-forming) that allow you to maintain higher bandwidth at much larger distances (or through thicker walls) than 802.11n. There are plenty of people constantly whining about how 802.11 gives them lousy speeds in their basements or gardens or whatever, who will see improvements from 802.11ac.
I'll await real world demonstrations of beam-forming before drawing any conclusions on this. Initial observation seem to suggest it has potential to not extend the distance a router can drive a signal, but rather better permeate physical obstructions.
That said, maybe you are forgetting that there are actually quite a few scenarios where the older standard 802.11g outperforms 802.11n due to physical barriers (walls) or distance between routers and devices? I'm not saying ac will be a downgrade, but I'm more anxious to see how this performs in real life before labeling it a game changer.
Louis CK does a whole routine about how people who don't have a clue how cellphones work feel happy to complain about how lousy they are. But whenever 802.11ac comes up, we see something even weirder --- a chorus of people saying "I don't want it to get better, nothing should change, all the engineers are stupid for trying to improve WiFi".
I mean, seriously, WTF? What is driving these bizarre complaints?
I'm all for having the latest technology, but aside from the potential of beam-forming (yet to see if this is actually going to work as well as theory suggests), ac really won't make a difference to iPhone users on WiFi. We aren't downloading/streaming 40+ megabytes of data to our iPhones, and as ac doesn't promise "further" distance performance compared to n, I'm skeptical of how much greater it will actually be in practice.
