It does seem that the TB dock solutions currently out there with USB 3.0 support cap out at USB 3.0 speeds of 2.5Gb/s - not sure if that's a hard limit, or just what the current controller chips are able to push. TB2 probably won't be any help; any machine with TB2 will already have USB 3.0 also.
I suppose someone could make a TB to USB 3.0 hub, even if the USB ports cap at 2.5Gb/s. Will they? Only if they think enough people would buy it. I don't know how likely that is.