Why no mention of the total lack of support for Echo Show devices? You say "vast device support". but apart from my TV this is the one device I would make use of (in multiple rooms) and there is no support for it. Not only that, but there is no support in the BBC Sounds app for streaming to ANY Echo device, even though there is a BBC Sounds skill. Honestly the BBC fall far short of services like Spotify even in terms of how seamless they make it to use their services.
yeah, the lack of 5.1 is a real puzzle. The BBC's position is "we think this is niche and people don't want it" - but when you have a choice of football in HD with 5.1 on live broadcast or UHD and 2.0 on the iplayer, that doesn't seem to stack up (expecting people to ignore a live broadcast to watch the football on a 7 second delay via the app seems a lot more niche).
Most people don't have the hardware for, or even care about 5.1 sound or Atmos as they just use the TV's own speakers or a simple soundbar or soundbase. As for picture quality, just had a look at Blue Planet 2 and the picture is excellent.