Lightning network implemented by exchanges might be a catalyst for Tether to go down. Why? If you are a small time altcoin trader, most probably you store intermediate gains in USDT before accumulating needed amount to move to an exchange that supports withdrawal to a bank account. If Lightning network is implemented and BTC transfer fees go down to cents, who needs Tether anymore? You can take altcoin profit to BTC, transfer it for cents to exchange that is backed by FIAT and exchange to that. That could mean massive decrease of Tether use. And Lightning network should go live this year as impatience is growing and there are already hundreds of nodes running in mainnet