I don't know about e-commerce place but I know some vendors that accept Bitcoin as a settlement of debts, you see them more in numbers during the bear markets, the Bitcoin they collect aren't for sale immediately, they hold it throughout and then sell during the bull run and they make their profits like nothing happened because they also understand how valuable it's to hold Bitcoin.

As for USDT, I'm not sure about it but I don't see the difference between USDT and fiat, why accept USDT as payment when you will pay more tax in crypto than when you can do it with fiat and pay small tax, also don't forget that USDT Tether is fond of suspending some wallet address they found suspicious, it's not a good idea to use stablecoin for your business, I will even prefer Bitcoin than usdt.