Sub-80 players will catch up quickly after the gold squish because they quest a lot and the gold reward from quests will be unchanged.
With all saved gold reduced by half, everything sold on the AH should see their price go down (since people will have less money to afford things and will not be willing to buy things at the same price as before), so newer players should be able to afford it with the quest gold.
My piece of advice to newer players: You have plenty of time to reach 80 before 2017. Do it, and spend 5000 gold for your 280% mount before your gold is halved. It's the best investment you can do.
You WILL have enough gold to buy it if you quest properly, properly vendor trash, and AH other items.