Introduce a way to eventually research everything

At the end of the campaign there is still a lot of items I did not research, while I like the aspect of choosing your own research route I would like to have the opportunity to eventually research everything the game had to offer. This could be done by simply introducing an endless mode at the end of the game to see how many days you can survive as more and more Titans swarm your base or something completely different. The point being I would like to see the addition of a way to eventually research everything so when playing a stage I could literally pick from every possible option.