Now that helicopters are functional as so far as flight is concerned, perhaps we can revist the wings mutations.
So, currently, both bird and insect wings don’t offer the ability to actually fly with the reason given that you are simply too heavy, but the bird wings are at least strong enough to allow you to glide.
So I was wondering… bird wings are not post-threshold, and neither are hollow bones. The tiny mutation, (which is post) if you start off at lowest starting height, puts you at 1 foot six inches and at 11 pounds for normal weight. (hollow bones are not accounted for.) I would imagine that at that size and weight, a mutant should be able to fly if they keep their gear below X weight. Anything above the weight limit means you simply cant take off, but gliding down is still possible.
Also, there are a number of mutations that are 2 staged where your anatomy “catches up” with the first bit, like cat eyes being useless until you get feline vision afterwards. Flight could very well be the same way like "your back muscles and skeleture have finally adjusted to allowing your wings to fully support your weight.
Now, granted, tiny and little would also make your wings smaller, and large birds do exist, but I put those 2 mutations there for balance more than anything else. But the UI could easily support the inclusion of flight weight right next to the current carry weight.