Annihilus could serve as a substitute for the Skrulls in my framework, if you tie their origin into the Negative Zone rather than space travel.
I know, I know, dozens of people right now are complaining about the idea of "yet another origin." However, my idea is that, if you make the origin itself an entire adventure rather than having it tie into some kind of 'ordinary life beforehand', you'd end up with something distinct. So, they do the experimental space flight, get powers. . . and then land on the giant alien spacecraft carrying the Skrull invasion force to Earth, and have to stop it. Or they do the N-zone portal experiment, pop through, gain powers. . . and then discover the natives, and their own malevolent schemes and have to stop them.
Basically, instead of "ordinary life, origin event, ordinary life changes", you have "ordinary life, origin event, adventure."