You both are assuming a scenario where supply stays the same and only item demand increases, but with gil now having a bigger purpose more people would get into the market to make gil for sub tokens. Yeah like mentioned before there would an initial dump of gil from people currently hoarding it, but the market should to balance itself once people start selling stuff for gil. This isn't the first game to add this type of system and all of your fears always end up being unfounded in those games.

I feel like an economy where gil is circulating is healthier than one where people just hoard gil for no reason, that's an unintended gil sink and I doubt the game is designed around having those massive gil sinks.