Personally, I see the world map as being interesting, but ultimately pointless. It's fun to see the bars tick up, but nothing much occurs from it, including the wars. Sure, having your name mentioned is nice... but meh? I suppose that puts me in Hamster's camp, but there are hose who DO heavily enjoy the map gameplay and playing hard in Alliance.
I personally don't see, logically, why a player would lose all of the gold from their faction, but I certainly see them losing a percentage, similar if not identical to the Reputation loss. You've been with the faction for x amount of time, gotten to x rank, you lose y% of gold. Flavor it as you will, you're a privateer who had to book it, you only managed to withdraw that amount from the faction bank, what have you. But Mechanically, the rule would be simple enough, you lose a percentage.
Caps... Caps I'm mixed on. 1: They *do* allow another level of achievement for each level gained in factions. The levels are so distant and annoying to grind for. 2: They *are* a major way to influence the world map, especially for those who just stick to PvP and don't grind in PvE. In PvP, you always get a locked, basic cap on how much you can earn every match, 200. Alliance, I believe, is the same, or at least close. The cap may be there as part of the leveling process, giving something for the player to actually enjoy receiving, as well as to encourage spending early on. The thought is that newer players will do worse, and so may gain less in coins. As such, their cap is lower, making them pleased and encouraging them to spend it when they hit the cap. It certainly locks them to lesser ability to influence the map, but it also means that they have more in the way of instant gratification.
tl;dr: Lose a moderate percentage on changing faction rather than everything, unsure on the cap, but keep/raise it slightly in order to keep it as part of the leveling process.