Personally I'm expecting transmog will only work on items dropped after they introduce it. So all the players that are saving cool bits of armor they farmed hoping they can transmog it will be screwed. Add to this there be some random currency that's not fun to farm but you need it to use transmog and we're set to go. There will likley be a bright dust or silver way to bypass this currency cost, of course. Don't get me wrong, I think that's pretty much the worst way to implement transmog and I'm not in favor of it at all, but this is Bungie we're talking about and they rarely land a new feature right. Or even remotely right.