My problem with that approach is twofold:
(1) with the exception of maybe CoIE, most DC Crisis stories are not highly regarded universally. My personal favorite Crisis story is Infinite Crisis, where Superboy Prime is the villain. But most people aren’t enamored with that story and even though Superboy Prime is my personal favorite DC villain, I don’t want him as a villain on film. DC thrives better in the more intimate, emotional conflicts as opposed to the grandiose galactic threats that lead to crises. In fact I’d say that even Darkseid works best in Fourth World as opposed to being a JL villain.
And (2) Marvel already did this with the Infinity Saga. Everyone wants DC to do what Marvel did, but why not be innovative? Why not do something different? The Marvel recipe that spanned ten years was innovative, but now it’s formulaic. I don’t know that CBM fatigue is as real of a thing as much as also-ran shared universe building up to big fight movie is a rinse-repeat formula that is tired. Honestly, the reason why CoIE is as popular as it is is probably due to nostalgia and the fact that when it came out, no one had attempted anything like it before. Fast forward to today where you can visit the comics forums on this very site and every time a crossover event is announced, we all groan because even in the comics, it’s a tired formula that ruins the allure of the character studies of the individual titles.