According to the digitalbits.com, Andy Parsons confirmed the BDA is going to look at the possibility of a BD-4K disc.
I really believe if 4K and quality will go together that the only real option is a physical format based system. Streaming 4K will either be limited in quality due to trying to squeeze it into the pipe and/or limited due the number of homes that have connections that can support it.
The reality is that just because Netflix/Vudu/Hulu/etc flag the content as HD/4K/etc doesn't mean that you are really getting all the video signal.
If it's a download model, how much space is someone going to need to store a large film library in 4K? 100TB or more? Sure HDDs get bigger but you still have an issue if a drive fails or something corrupts the drive. At least with a physical format if something goes wrong it is usually a disc or two that fail which doesn't render your entire collection unusable.
Now my main concern is if the BDA is going to do it right. Remember when the DVD Alliance tried to convince us a DVD9 with newer codecs would be sufficient for HD? That thankfully quickly changed due to competition. Instead the battle between the formats ended up giving us a disc that was truly intended for HD content.
So the BDA needs to look beyond the 50GB disc. They need to look at the BD-XL data disc variant along with newer codecs. If they try to cheap out and just meet what can be done over streaming/downloading then the product might be dead before it gets to market.
They have time to do it right. The first HDTVs went on sale in the late 1990s, but they weren't affordable for most until the mid 00s and that's when we got the HD formats. 4K sets are going to be in the 'rich only' club for several years. So the BDA has time to come up with a format to deliver the best 4K experience.