Sitefinity 4.x should support all possible video formats, as long as they are playable by Silverlight. In order to enable the .mov and .mp4 extensions go to Administration -> Settings -> Advanced -> Libraries -> Videos -> Allowed file extensions and enumerate the extensions that you need separated with a comma. The recycle the app pool and you should be able to upload such files.
Sitefinity's RadMediaPlayer (the one we use to play the videos) supports the following formats (not extensions but codecs used to encode the file with) -
As for the streaming - there is a logged PITS issue that is related to this problem -
You can vote for it.
You raise an interesting question here. I will make sure this matter is discussed with our architecture and UX teams so they are aware of the future possibilities. The problem here is backward compatibility - even with the Release of Windows 8, it will not be adopted right away and we will have to support two platforms anyway.