Perhaps the iPhone should autoplay videos, but muted until you hit a speaker icon (or something). Either way, forcing everyone to use GIF is horrible because of how inefficient it is.
I'd like a global option and also some simple per site UI.
This is how the click to play in Firefox works, it's nice. One thing I haven't figured out how to do is trust embeds from a site (for example, Youtube and Vimeo both have well behaved embeds, so I'd like to whitelist them, but not many of the third party sites I see them on).