werent the xbox be able to go from 720 to 900p after they did similiar things? Maybe it will give a huge performance boost to realize 60fps for some games
Nope. 720p to 900p was after freeing Kinects GPU reserves. That ate up to 20% of GPU performance AFAIR.
CPU time also was reserved for Kinect in the beginning. So MS' first step was reducing the system load Kinect had. Then they freed up resources from the seventh core, which might have been one reason a few games had better frame timing/less framerate drops on Xbox than on PS, the CPU already cloccks slightly higher. That usually was with games reaching 900p on One and 1080p on PS4, so no change on the graphics front here.
Right now we're likely getting to the point where all possible resources are freed for games. Both will need one core and plenty of RAM for multitasking, background stuff like snap functions etc., so some tweaks might still be done, but all the big steps are already made.
Doesn't mean they can't tweak their systems anymore though. Both will keep on working on their API's and so on.