I would rather it have a way to buff the next GCD, since well, we are already pretty tight GCD wise...
Adding just one GCD skill totally messes up my rotation, at least :/

For example:
If the way to increase Huton duration is really a new GCD that extends from Gust Slash, then every time I was supposed to use Aeolian Edge would be replaced by this new skill, depending on if its also potency/TP-wise-worth. But there is a risk of never again using Aeolian Edge this way.

If the new GCD actually extends from Shadow Fang instead, it looks much more friendly and healthy for the NIN GCD rotation, imo.

Im still crossing fingers for positionals to be the ones that boosts Huton's duration, since that would be more interesting. For me, at least.