Yes, I made it. I can import video files in LR 5.2 and make use of the new features.
During the last week I daily downloaded and installed 5.2 just to find out that video files were unimportable and didn't show up..
Today I did exactly the same as all the other times and somehow it finally works.
Don't ask what was different - a unique good version of the download, a fortunately good connection with Adobe, an unexplainable constellation of hard- and software circumstances?
Anyhow, I'm up to date now and can only hope or pray that the next time things will take less time and confusion..