Given the current smart connector doesnt support general data use a snail with a floppy glued to its back is faster than the smart connectorThunderbolt 3/4 is still faster than using smart connector and plus there is no advantage in removing USB-C on iPad.
I assume that with 4 pins they’ll probably be packaging a full usb 3 or 4 layer with it, so it could be pretty fast. It’s not going to replace the USBC plug though no matter what, there would be no advantage to that, so this whole debate is silly