I dont think there's a need for them to integrate USDT since they also offer stablecoin which is even better than USDT and with my findings it only BTC payment that currently have problem it will be better if people choose ETH which they later swap to BTC through myether wallet or an exchange.
The usecase for USDT is GOLD is a stable one but it has not yet been listed on too many exchanges. In turn, people have to convert their GOLD to ETH if they want to move their funds to exchanges to trade. ETH, itself is not a stable altcoin. Having USDT is good, and if it is not good, it does not bring anything bad to the GOLD marketplace, in my opinion.
If there are not many technical issues or requirements to integrate USDT on GOLD marketplace, I expect to see it later.