Would there be a way to implement libVLC as a replacement for Quick Look in Mavericks and Yosemite? That would be fantastic!
Right now (as you may know) Apple depreciated Quick Look and it no longer works with far too many video formats even if one has the old version of QuickTime installed with Perian.
Quick Look's media support is pretty sparse, but that's due to its use of Quicktime X for most video and audio. QL supports plugins from third parties though so... yes. You don't need to replace QL, just build a plugin for it.
See the post at the bottom of the link above. In a nutshell, things like Perian that used to allow Quick Look (not to be confused with the QuickTime Player) to preview a bunch of video formats got hosed when Apple switched over to "AV Foundation" or something.
Considering how many less video formats work with Quick Look after "upgrading" from Snow Leopard to Mavericks, I personally consider it "depreciated" at least in principle.
Quite a lot of Mac users (especially those that work with a lot of video formats) have been waiting for something to fix this Quick Look issue for some years now.
The best you can do at the moment is install this to see thumbnails in Quick Look for some video formats:
Do note that current plugins for Quick Look video do nothing more than be able to display static thumbnails of various video formats even if you have Perian installed. Unlike with Snow Leopard and Perian in the past, you won't see the actual video and audio run in Quick Look with AVI, MKV, etc formats.. That's where the libVLC can come in, I hope.
Right now (as you may know) Apple depreciated Quick Look and it no longer works with far too many video formats even if one has the old version of QuickTime installed with Perian.