Someone sneezing too hard is enough to destabilize the economy for weeks on most servers, any time someone new pops up with something to sell it immediately turns into a war over who can sell their silver ore 1 gil lower than everyone else that eventually tanks the whole market

Honestly what you should be thinking about if you're a merchant is how to take advantage, the prices on a lot of very expensive things could possibly tank for awhile, but then they will go back up as people settle into the new system, at which point you can make a killing selling it all back to others, that's business.

I'm not ashamed to say I've made characters on different servers entirely for the sake of buying things there for up to half the price or more compared to others because honestly I don't want to spend more than I have to

I've also made characters on stupidly overpriced servers for the sake of crafting and selling a ton of stuff to make gil which I then took with me via server transfers >.> not having to do either of those things will be nice, as will being able to buy things for a fair price.

It could also go in an entirely different direction though where the sudden burst of people switching between servers to buy things causes the prices to skyrocket to keep up with the demand, then it will steadily decline.

Either way it won't take long for things to settle down

Fieldcraft Demateria III's used to sell for up to 100k each in minutes, now you're lucky to get 30k for them and it's not even really worth selling anymore, the market will always be that way