I think another point worth noting is that trillions of gp in wealth will be wiped out by the devaluation of many junk items that currently have some sort of price. As we're also beginning to see, rares are falling across the board. Santas, masks, easters, and soon disks and pumpkins will be selling min in the g.e. As for partyhats, it's too early to say.
There's less actual gold out there than it might seem. If you want to be best prepared for the update, I'd keep as much gold liquid as you can, buy a few pvp/pk items if you want since those will certainly go up in demand. Who knows when the update will actually happen though