apng SHOULD use a different extension other from the normal png (i recommend apng, ALL OS our day accept more than 3 letter extensions)
something that many people hate is note being able to see that if a gif is animated or nor, unless we open it via a animated gif capable program... doing this with png is repeating the same error, its hijacking the png format.
anyone that dont have a apng capable program could rename it to png and see the first frame, but trying to tell to the user that a apng is just the first frame is lying and breaking many programs without the user known anything about it.
apng with the .png extension is BREAKING the png.
the .gif world is a mess because of the netscape mistake, please dont make the same thing to the png