I'm no expert, but...
I think the limiting factor in these things isn't optical resolution, but the ability to compensate for atmospheric and other distortion, not to mention adjusting for orbital motion. Imagine trying to track something the size of a shoebox long enough to take its picture. Every try to track a moving object with a binoculars set to highest magnification?
I don't think these problems are unsolvable, but they do matter as much as the size of the mirror.
R.L. should weigh in on this.