Because I like being able to improve those too, I added some code for Robot Cargo Size and Stack Inserter Bonus.
I figured cargo size is really OP, so I made it cost 3 times as much each level (rather than twice), and consequently limited the levels to 10 since higher levels cause strange problems with the research cost.
I made the stack inserter go up by 2 every time (like the last several vanilla researches), and the normal inserter bonus go up by 1 every 5 tech levels (starting at 10).
I'll make a second post here with the code, if you wish to copy it. The hardest part was the if statement for whether or not to increase the normal inserter bonuses.