It's a bit silly to say that "The Avengers" is not future-proofed though -- it looked great on a big theater screen. Many older 35mm titles are not going to resolve 4K worth of measurable detail either but one isn't going to say that they aren't future-proofed because of that. People rarely decide to re-watch old movies based on how much resolution they have. Does "Casablanca" resolve actual detail at 4K? Does "The Godfather"? Do those movies look sharper and more detailed than "The Avengers"? And what about movies shot in Super-16? No future for them?
I also saw some of "Think Like A Man" projected digitally before I went in to see "The Avengers", and that was shot on the Epic -- it looked great, but it was shot with Classic Softs and net filters and there is no way that the image is 4K in resolution even if it were mastered at 4K. So you end up seeing two movies, one shot at 2.8K with no diffusion and the other shot at 5K with diffusion, and the end result is about the same level of detail, so why is "Think Like A Man" future-proofed but "The Avengers" not?