Maybe its none of the above
I'm cautiously hopeful that this might be a precursor to rolling out HEVC coded videos. But I could be completely wrong. I have no concrete evidence other than watching what the video industry is doing and certainly no inside track on what Apple is working on. But, let me explain why I think this is a possibility. Then tell me I'm barking mad afterwards.
When AVC/H.264 came out, it was twice as good as the then MPEG-2 video we were used to on DVDs. AVC could cope very well with 1080p and made it feasible to roll out Blu-Ray players and downloadable HD trailers on the web. As encoders have gotten smarter, the bit rate has come down steadily just like MPEG-2 encoding did. HEVC is the next step which adds some new tricks to video coding. According to industry experts who spoke at NAB and IBC conferences over the last 12 months, its twice as good as AVC. Or to put it another way, half the file size for the same quality. It is designed and optimised for two important goals. Cope well with 4K and then 8K video frame sizes and deliver smaller frame sized video to mobiles in a very compact and fast (low bit-rate) fashion. And we expect HEVC to improve over time so that it might eventually accomplish the same quality as AVC (Blu-Ray) for a quarter of the current AVC bit rate given enough time for the encoders to mature. There are still more coding ideas beyond HEVC that have yet to be tried and proven.
Now, we have WWDC starting in a day or so and that's usually where we find stuff out about major seismic changes to OS X, iOS and QuickTime.
This is pure speculation, but what if one of the so far unmentioned changes that we might see is HEVC everywhere. Wouldn't that change the scenario for downloading 1080p on not so fast Internet connections?
But as I said - I could be completely wrong - and we only have a day or so to wait and see.