A difficult part is finding iconic material, finding what can ideally be made into icons. I tend to want to abide by the rule of making them unique and distinct even in low resolution such as 32×32 pixels, since I am still using an operating system nearing a decade old, so a major impetus for the icons set I made was definitely to selfishly have an icon for each of the animes I had seen, at the time.
Maybe I just haven't been digesting since then enough anime that have abundant, readily-provided iconic material. In the end, we could all benefit if good iconic material existed. Making icons of characters themselves is sort of a cop-out default plan, but even that could work. If this is easier, why don't we see more of this? Maybe it's because we're lazy xD
That said, if we can organize some sort of effort to make an icon factory happen, I'd be for it. It may be technically difficult (because of file formats and multiple sizes) but it's not much more than typical avatars, I think. The reason why I would be against this is because I want icons to be deliberately designed—well-executed and well-associated with whatever they symbolize, and fear similar ideals/standards may not arise from a group effort; then again maybe I'm going about this being overly elitist and srs.