A cryptocurrency with demurrage tax would fall directly on holders, and therefore hopefully discourage hoarding. encourage dumping.
there i fix that for you
There will not be any dumping if there was no hoarding in the first place.
(And, as I wrote, that is one of the problems that bitcoin has: so much of bitcoin's mass is hoarded, that the price could crash in a blink if even only 10% of the hoards were to be dumped.)