I don't expect this to go over that well, but I'll point out a few things.
First, to get the obvious out of the way, ethnicity swapping characters is dumb. If you want to have a more diverse roster of characters, why not simply use of the many minority characters already present in the comics? Like it or not, Spider Man is Peter Parker, having someone else be Spider Man for a few minutes is an old gimmick (done with a lot of characters) but the whole point is it's NOT Spider Man and it works because the status quo is restored. Spider Man and his identity are pretty iconic right up there with Clark Kent being Superman. Really the only real reason to use Miles seems to be to make liberals happy by replacing an established character, and of course generate hype from the controversy.
See, from my perspective if your going to bring out "obscure" characters to begin with why not say do "Cloak and Dagger" a couple of characters with a decent cult following and who have endured for a long time now. Cloak is black, has a unique power set, and does the heavy lifting (ie most of the cool stuff) of that particular duo. The thing is that Marvel has a pretty diverse roster of characters, and is hardly a "white washed" roster even before political correctness set in. If you want diversity in the movies, why not use any one of the legions of awesome minority heroes out there and give them a chance? Ethnicity swapping is lazy and seems to be intended to bait controversy and play to particular political sentiments. What's more as long as that kind of garbage is going on it reduces my chances of ever getting to see a decent "Cloak and Dagger" movie.
Second, let's be blunt... Milo is hated by pretty much everyone. That's a controversial statement, so I will explain. A recurring joke in a lot of comic communities is that Milo has the most successful comic that nobody ever reads. The reason why that's "funny but true" is because of people who buy it up specifically to get the run as part of their Spider Man set in hopes that it will be worth something some day, in the sense of being there 20 years later and saying "hey I've got the whole run of that black spider man they did". In terms of critical reception in a hardcore Marvel nerd community like the game "Marvel Heroes: 2015" where people will drop $10-$15 on an enhanced skin (different voice and animations as well as a simple skin change) to represent a very different version of a character, the idea that there is going to be a Milo Morales skin "any day now" is a recurring joke, you won't see one because nobody will buy it, even "Spider Gwen" which is a 15 second gimmick concept if there ever was one is getting an enhanced skin and it was even being promoted for pre-order. Really the only time you hear anything NICE said about Milo is in an article like this where the point revolves around him not being white and what a great thing diversification is, part of that is that at the end of the day he's nothing special other than an ethnicity swap. Basically, he's a purely political phenomena, something I expect to hear about for that reason for a long time, but not anything that is likely to have serious comic fans, rallying to see more of. If Milo was a good character it might be different, but that's half the problem, he's one of the many, many, dumb things "The Ultimate Universe" is known for, but one that seems to have struck a political chord with some people. In comparison take say "Superior Spider Man" which was Doc Ock as Spider Man, he was very divisive in terms of people liking that idea or hating it, but it was a different enough take on things that it stood out for a while. Milo in comparison winds up doing much the same thing as Spider Man for the same reasons, except now he's a minority.
Also I'd point out that a lot of the other changes people are talking about aren't what they are being promoted as. For example the whole "Thor is a girl, it's actually Thor, not some clone or someone hero worshipping him" is nothing really new. It's been downplayed in comics recently but something people tend to forget is that Thor is pretty much a possessing entity backed by some reality warping logic that can arguably cause Asgard to conform to him to an extent. Thor is actually the entity Thor living inside a man called Donald Blake who happened to find the hammer. Classically Donald would wander around as a cripple with the hammer disguised as his cane, and then tap it on the ground to become Thor. As time went on though they started to get away from the whole "secret identity" bit and him sharing space with the mortal who found the hammer, although every once in a while it would come up, for example in "The Infinity Gauntlet" some might remember a bit where Thanos disarms Thor and causes him to revert to a mere mortal, sending him drifting through space without the hammer, where he starts to die, however he gets his hands back on it and changes back into Thor and then re-enters the doomed battle. Rebooting the universe is a good time to re-introduce this forgotten aspect of the character, through which it is indeed possible that Thor could be a girl, if one who was worthy picked up the hammer, his appearance would become a hybrid of his and hers. One of the more extreme cases of this was when I remember a Frog briefly wielding the hammer as Throg (as a joke) but that was a long time ago and I'm fuzzy on the details. Thor has had a few different bodies over the years, and to be honest I don't think they will keep the concept as a dude and a dudette sharing space permanently. To me that one struck me as a stunt intended to get the goat of people who just don't know the character very well, such as people who only know the character via the movies without ever having read the comics and probably couldn't tell you who Donald Blake was to save their life.
That said, at the end of the day I don't know many serious comic fans who would like to see Milo get a movie or a permanent role in the comics if this reboot happens as people expect, compared to say some of the cooler minority heroes being given a shot. I also anticipate that Marvel knows that if a video game company doesn't even see a market for a milo skin (who knows, maybe one day) it's not going to be putting that much of an investment into the character.