When I released my mod I moved it over to my server to try it out...
Then I quickly found out that the default 6% which was the value for v1.0 was insufficient to prevent the player from taking fall damage. (Increasing it to 10% proved effective at preventing the player from taking fall damage, thus my change for v1.0.1 is 12%)
Upon thinking of ways to a better solution I figured implementing 1 or more of these methods may "do the trick" so to speak:
Adjust gravity (this gets ugly quick, I'd have to track who's using the feather so if they stop then return them to normal gravity, else leave it alone, and other mod collisions if they play with gravity)
Keep changing the force we apply to counter velocities (which is okay, so long as we don't exceed 50%, then we start making the item cause players to float upwards)
(I forgot the other thing I was thinking of, at some point this will get replaced with my other idea I had)