It’s a good mix of a client and server-side issue—I’m working on this in my client at the moment. The article images are already provided by Lemmy instances, so that‘s no problem to implement. When it comes to video, that’s gonna be a harder challenge to tackle. Reddit, Twitter, Facebook, etc. all have their own dedicated and high-powered services that handle and process video to give it the ability to preload and instant-play. Lemmy does not store videos that are linked currently, and it’s tough trying to implement video support when all you’re given is a foreign link that tells you nothing about the video. If it’s a huge video, it might take far too long to load. And when it comes to YouTube, Vimeo, and other services, the only way to embed the video is using their own player on the website, bringing up huge privacy concerns.
That said, It’ll be fun to tackle the problem, and maybe down the road Lemmy devs can find a server-side solution that will speed things up and maybe preprocess video links or something. It’s only up from here!