How would increasing the gil cap resolve the stated problem of players at current gil cap not having anything to do with all their gil? All you've done is give them more gil with nothing to use it on.

This is of course ignoring the absurd premise that players at gil cap are at all the source of any significant amount of RMT sold gil.

It's far more likely that players at gil cap are more willing to just dump it on any old random thing without a second thought, because those are the players that most easily return to gil cap. They'll be the ones literally gambling away millions on something as simple as a /dice.