The coming will be a disaster for USDT if they continue to develop this way. Globlacoin is certainly more prestigious and the transaction fees are much cheaper. In the near future they will have to compete with a very big competitor and I think this will really cause big losses for USDT. Market share will be stolen by Globalcoin.
USDT only exists within the confines of crypto exchanges. It doesn't have any use or purpose outside that. USDT's main appeal is their indifference to compliance as long as you stay within it. Facebookcoin will be a very different beast and we don't know whether they'll allow it to touch any exchanges beyond their approved ones, and even the approved ones may only allow exchanging to proper fiat currencies.