Yeah I agree that it could be gradually introduced, makes sense - for what little our opinions matter!!
Certainly not my thought process or desire to slow down higher GP players. I think with any change there's always a short term pain. Initially higher GP players would be at a bit of a loss in terms of resources but presuming there are plenty of places to farm/aquire the new piece then before long they would be back to having stashes.
I think it depends on the intention CG has for a bottleneck on those kind of pieces (current or any new way). Not meaning that in a critism of CG. If it's specifically aimed to affect players not so far into their journey then the status quo would quickly return to normal. If it's aimed to slow everyone down then it currently doesn't do that anyway? Just the players they are actively trying to make it easier for currently. Tbf I think the answer to their intention kinda shapes whichever argument.