[Praesten]

I don't know how to debug the log and I'm not expecting an answer right away. So I think my question is perfectly reasonable. As I said in my original post: This feature is 'advertised' as being part of the new version yet some people say it's really not. So perhaps the specific answer needs to be documented somewhere, e.g. on this support forum?

Go to Settings -> System -> Debugging -> tick "Enable Debug logging".

That gives you (in Linux) a file inside /home/username/.xbmc/temp called xbmc.log which is logging as much as possible. You don't have to debug the log, you just have to open it and search. Or just do the following:
grep -i vaapi /home/username/.xbmc/temp/xbmc.log

Replace username in both instances with the username of your XBMC-user.