Inflation can easily occur overnight.
lets say you have 30mil
And its christmas eve
RMTs sell gil for $1 per mil
Billions of stored up gil pour into the economy

Your 30mil which could have bought you some of the best gear yesterday can now buy you a single-melded upper tier bow only....

Thats what happened in ffxi and it will almost 100% happen here since there is so much gil "stored" up. The economy is only smooth now because people horde gil so that if they release something like dynamis weapons they will have tons of gil stored up.

Once there is something for them to spend it on, they (and prob ppl buying gil from rmt) will flood the current servers with massive amounts of gil which will cause prices to skyrocket.

And then if they try to "fix" those servers they will hurt the new servers in the process
UNLESS they treat servers differently, in which case there won't be any problem.

The problem arises when you try to fix inflation on 6 servers and effect the 3 non-inflated servers in the process.

This happened in FFXI and there was much less gil stored up. So it's very realistic and likely