Most sites create a thumbnail for you. Why not let the user have the option of adding a direct link (ie; youtube thumbnail url) or adding it from their own system and resizing to a specified size in the admincp?
I imagine that would be quite easy for someone like you to add. If I knew how to do it myself I would, but I don't :)
Also thumbnails for categories perhaps the latest added video thumbnail is the category iamge (similar to IP.Gallery) and a preview thumb for each video inside the category also.
Someone suggested lightbox videos.... I don't like that idea. I use lightbox and videobox on sites I make, but I don't think it'll work good for this sort of thing. Youtube or any other major video site use it? Enough said :)
As suggested already I think the "video portal" and hooks are a great idea. I can't wait for the next release.
Have you looked at ttmods video modification? May give you some ideas. It works with ffmpeg or mencoder, but it has a portal and all the jazz. I used it with IPB2.3, but it's not updated and may not get upgraded to IPB3.x so I bought this instead. Check it out below anyway.
http://forums.invisionize.com/ttVideo-v100-Youtube-Clone-Component-t133594.html