I've never been a fan of rng proc based abilities.
So I like the idea of this change, but it would hurt dps even more if im understanding you correctly. unless you meant every one of the moves alone always guaranteed a feather.

TBH tho DNC doesnt need really any flow or QoL changes, but it does need a dps boost.

Thus to me the best thing that would be a simple change would be to move Saber dance to a oGCD, this would be a significant dps boost, and would raise the skill cieling slightly.

Beyond that these are the changes I'd make:

changing your idea a bit. Make it so using both single target flourish skills guarantee rather than random procs a feather. And both aoe flourish skills guarantee a feather. THe effect would be the 50% chance was removed but still required two moves, thus being the exact same average dps and removing one rng proc involved in the class.
This is hard to explain. trying again more clearly
To gain a feather one would need to use reverse cascade AND fountain fall. Proccing and using a second reverse cascade before using fountain fall would gain nothing.
This would slightly nerf dps, slightly because originally each was a 50% proc. now it requires two moves (maintaining the same balance as the already earlier 50%) but occasionally a proc might be wasted because of the randomness that enables them from basic fountain and cascade.

Then finally i would make feathers always trigger feather flourish, which again would remove a random proc and boost potency of the class again a little.

Also add a small dmg buff to en Avant so the dancers movement itself has to be placed properly to perform at its skill ceiling. by adding a small aoe dmg strike to the impact zone of en avant with its 3 charges dancers would keep two for mobility, but try to use the the 3rd charge on cooldown with positioning in mind to dmg the boss.

So in summary:
-Make Saber oGCD without potency loss, its meant to be strong, this is the main potency boost.
-remove feather procs randomness, slightly boosting the skill ceiling, while nerfing dps very mildly.
-remove feather flourish randomness, slightly boosting dps, and again removing another random proc.
-Add aoe to landing zone of en avant, making movement and dancing not just an escape effect, but an actual part of dancers dmg output.