Re: Will the H.264 decoding have a linux driver?
That mailing list discussion is about yet another API for video. It does not automatically lead to a working implementation (although that Intel guy might write something for Intel devices).
I think the problem for now is not the API. We have APIs to choose from already.
The problem is to go from "you could write an H.264 decoder in GLSL" to a working and re-distributable decoder. That is not a project for a rainy sunday afternoon, as far as I understand.
Once that decoder is available, attaching it to an API or directly to a video player program is the trivial part.
The discussion also mentions that using GLSL would mean it can't work on very old cards (although I don't see the problem with that...) and that new cards apparently again implement the dedicated video decoding hardware that has been omitted in the previous generation. Which would mean you want to use that hardware, not the generic shader engine that GLSL would use.