Originally it was said that these sub brands were to get around the regs of producing xx amount of hybrid/EV except Seal used Cupra as the spring board for the EV segment which I think will bite them later on when they want to bring something 'hot' to the market if that day should ever come. But you are right, when did you last see a new Seat, I can think of anything I've seen recently or what their new models look like tbf?
Keeping Alpine and RS as a sub brand will always work in Renault's favour. I'm sure there will be a revival of the RS brand and a full RS, will it be a hybrid with electric assistance more than likely, we need to remember only the performance brands have used the EV side as assistance up till now and the whole EV is still relatively in its infancy. As it matures and brands get more confident with the market they will introduce new things and we will see a 'hot hatch' again only this time it will be a hybrid.
I also agree I don't think many have bought into the whole alpine thing and looks strange when you see the new lineup with 'alpine line' on the wing instead of GT line or RS line, non of which have been canned yet as far as I'm aware.