But I remember when USDT-ERC20 first appeared, its withdrawal fee was only 1 $, so I don't know if USDT-TRC20 will increase its fees like that later.
I don't think so, because TRC20 does not use gas like ETH, but maybe there will be changes if there is an update that requires sending USDT on TRC20 network using transaction fees, it is very difficult to make predictions in crypto because the development is so fast.
Thats true, and moreover a lot of dev teams are really afraid to give any hints about their upcoming updates - it may be simply stolen by competitors.
You can check out road map of a project, but we all know any project can add any updates in between the lines.