It would not need to cede any authority. The Texas grid already has interconnects with the East, West, and Mexico grids at four different interconnections, and imports/exports electricity through them continuously, while still having its own regulatory authority. The person you are replying to is suggesting to increase the capacity of these interconnects.

There was/is a plan to create a large hub for sharing up to 30 GW of electricity between the East, West, and Texas grids, but unfortunately it was scaled back significantly: https://en.wikipedia.org/wiki/Tres_Amigas_SuperStation