This is an amazing idea! I have done some research about this question:
Would adding gifs increase loading time significantly?
I found a super good and clear site that explains this. Right now, the iPad and iPhone saves image files as JPEG or JPG (.jpg). If you are on iOS 11, your device might use a new “.HEIC”-file format, but other than that, it would be a JPG.
Comparing JPG to GIF, the website I found says that JPG is the best file format for pictures, but GIF has some really good advantages like that it doesn’t get blurry when you zoom in on it that easy and that it is really great for details. On an example shown on the site, that was clear, however, the JPG image was about 5 times bigger and it got blurry when zooming in. So it won’t probably affect the file size to much.
Photos and pictures however, makes the GIF a second alternative as JPG has a file size of about 2 times more than JPG without any better quality in an example.
So, GIFs are better sometimes, and to make it real effective, THT could add a feature so that the app tells you about these differences in file size when you upload a GIF or a JPG.
Here are the link to the website that I used for the information: