Not sure. I think videos would be very expensive on the servers so I wouldn't expect it anytime soon. For now I hope they'd just add better embedding support so you can watch videos without leaving the website.
There doesn't seem to be any open PR related to video, and that's where most features are discussed. You could post it as a request and see where the conversation goes.
Logistically though probably not. Unless they keep it super restrictive like 15-25mb per post, and at that point why bother? Since instances have to store their data, adding videos on top of that would be an absolute heap of file size added to the 'cost' of hosting an instance. Depending on how Lemmy would handle sharing the video itself, the hosting server would have an insane amount of network traffic to stream it to users.
Lemmy servers with just images will start having a larger and larger footprint over time. Adding videos would essentially shoot that up like to an exponential level. It might not be a never say never thing but as Lemmy grows network traffic and the size of the data it needs to hold onto will be the choke points. They could work on it and make it something instance users opt into. But considering it'd be super rare someone would want to front the cost to host videos for their server it's probably more likely to make the integration with other video hoster websites better.
The fediverse doesn't federate videos and images though, they just share the link. Only the instance that got posted on would store the content while other instances would link to that image.
That doesn't seem to be true just from looking at some of the posts on here. Sometimes it's a link to the home instances image and sometimes it's a duplicate on like Lemmy World's server.
I edited my message just in case but it does seem to go either way on linking to another server or making it's own cached copy. The documentation on how Lemmy's implementation of federation works is like two lines in the official docs which is a bit annoying.