I'd settle for turning the trackpad into a second display and supporting Apple Pencil input. I'd keep it turned off most of the time, but it would be amazing to be able to flip it on and have it zoom into part of the main display in order to handwrite or draw something now and then.

You can essentially already do that by using an iPad in sidecar mode.

Which is honestly super cool! However, I don't have an iPad, and given my use cases, I don't need/want one that much. I feel like the Apple trackpad's unparalleled touch input would be perfect if it also served as a second display... I guess the right answer is in fact an iPad, with that extra real estate for drawing.