Thing with file formats is the libraries that you need to have in your server and the more formats you support the larger collection of libraries you need. Anything related to video needs stuff like ffmpeg and whatnot, which means that for those without server access you need to add php polifills which also increases machine usage. Since those are files are larger, you also need to code a queue process for it.
What I'm trying to say is that is not just touch some lines as some may think. Some developers maybe do that, like just check for mp4 at the end of the filename and don't validate anything. Put videos mixed with images... garbage. I don't work like that that.
This system will be always about images but at some point there should be support for trending formats like webp, webm, mp4, etc but not now because this is an image hosting script and customers expect improvements on that, not mutate the system into some image video hosting.