The notion of a live-action Pokemon movie is something that I find really interesting. Before I got into specifics though, I think they'd have to ditch the regular anime style..... No, not make it "mature", but at least make it to where it can appeal to all ages, and not just the 8-year-old demographic. Pokemon Origins did this quite well; it was still obviously kid-friendly, but it didn't feel like a glorified Saturday morning cartoon. I have tons to say on what I think a good live action movie would entail, but I guess that's for another topic.
I could see Cameron doing a good job.... If he would ever do it. Avatar boasted some incredible visuals, something I feel that could be translated to Pokemon well enough (what I mean by that is the Pokemon themselves being turned into 3D CGI). The plot would have to be completely separate from the anime, but I found my favorite parts of the anime back when I watched it were the gym battles and Pokemon League tournaments. If the plot was limited to, say, the way the tournaments are implemented in the show, I think the plot could work well enough. Although I find Cameron rather overrated in some aspects, I believe he's capable of taking what he's given and making a good narrative out of it.
Of course there's others though.... but I'm not too familiar with the world of directors in general, so my knowledge is limited I guess.