4K might be nice for the big screen, and the other applications that have mentioned. Still, depending on how you plan to distribute, it's not necessary. Netflix and Amazon Prime demand deliver to be in $K, but if you're using YouTube or Vimeo it's probably not necessary. Upstream Color was shot on a Panasonic GH2, and it doesn't look bad at all.
Thanks for posting this. I like the way it looks. I figure the look can be softened (if I so desire) w/ older lenses. The colors look good.
Creative Cow is a great resource.
I think the BMPCC has a 3x crop, so a 17mm lens would give you the "normal" field of view.
I have a Panasonic GH2 and an Eos M. I've shot a short w/ the Eos M. I love it. The color is nice straight out of the camera w/o doing much in post. I use it w/ several vintage Nikon lenses. It takes great stills also.
Wouldn't the conclusion be that you can make a good film with a number of different cameras; since the film wasn't ruined?