They could, in theory, have a "power saving" mode that tries to consolidate as much as it can into as few memory modules as possible (I'm currently using about 39% of memory, the rest being free and cache), virtual addresses would remain untouched and only physical addresses would change after a move and then it'd be possible to power down the memory modules that are not being used (PCIe-attached storage is slower than memory, but fast and power saving don't go together that well)

OSX is already proactively compressing memory in the background, if it deems a process worthy of compression.

Isn't it compressing caches only?

Probably would help if they freed up space and battery life by not having a totally unnecessary second screen taking up the top row of the keyboard.

And replace it with what, function keys? Keys which are thicker than the screen that replaced them and has far more functionality in a smaller footprint?