Update April 26, 2016: We’ve heard from developers, the limit per person will be 9,999,999 gold. It concerns the characters, banks, transactions, auctions in the auction house, etc.
Blizzard has decided to change the limit of gold per character. Remember the release of Cataclysm, the historical limits of 214,000 gold had given way to that of 999 999 gold.
Today with mounts and services offered always more expensive, it became tedious to transfer the gold between characters.
In practice this will profoundly change the prices at the auction of the Black Market since they will not be limited to 999 999 gold and the price war will flare.
For other services such as the sale of services and goods between players (Mounts, PL raids, etc.), it will mainly Blizzard to act effectively to scam the seller. GMs will not have to watch all the gold movements performed on the character, but only the final transaction.
A question remains: but what is this new limit? … I have yet not the answer! Only a few screenshots available on the Internet showing the amounts to just over 2.4 million golds. We bet that Blizzard brings us an answer quickly!