This is very intriguing to me. I believe early quotes were that (something like) 30% of the CPU was used for decoding, visuals, etc. leaving "plenty of headroom" for user apps and the like. Has this changed?

If I understand correctly the player software uses real time scheduling. The result of this is that it grabs basically all available CPU in case it needs it. It may only use 30% of the time it takes, but the rest is wasted. In order to get any significant cpu time another app would need to use the same scheduling method. I don't really understand the details though and I always wondered if it could somehow be set to take a fixed percentage of the CPU leaving some time for other apps. FWIW earlier versions of the player software also kept the load near 100%.

-Mike