This was suggested to death. Maybe less than multiplayer and planetary missions, but it’s a common suggestion.
Heck, I even made a summary and collected all arguments for it:
Chicken Invaders Universe episodes DLCs framework
While I can agree with CI1 due to few reasons (it already kind of exists in CIU and also it got a remakster(idk how to exactly classify it) not so long ago, ekhe, because somebody’s scared of open-source). Why exclude CI2? It could also be a worthy expansion DLC and it would be certainly fun to play CI2 on new engine.