If tonneau over was roll top or bi-fold/tri-fold, it wouldn't be any more expensive than those currently on 'compact' trucks.
Just have partially unrolled/only two sections when bed is closed; then completely unrolled/all three sections when extended.
Tonneau is to keep my hockey gear safe after a game when we go to the bar to celebrate/drown sorrows. Wouldn't want equipment in cab.
A cap is a little more complicated; but if Hyundai can make the bed extend, someone will make an extending topper.
There are topper for Dodge Rampages and Subaru Bajas.