I'm not in the least bit optimistic that BD 4K (or whatever it eventually winds up being called) is ever going to take off in the consumer market. For one thing, it's really only the cinephiles and the like that are going to truly be interested in something like that, especially if they cost anything more than $15-20 / movie. 4K televisions have no need of native 4K content to get Joe Six-pack to buy one from Costco. All they have to do to seel them is point out how they can "upgrade the picture" to 4K and put it on an 85" screen, all for the cost of what he paid for his edge-lit 55" LCD 2 years ago.
Streaming services like Amazon provide 1080 content already and consumers are flocking to streaming services. If the image can be "upscaled" they'll be sufficiently happy that they are getting the picture quality they should be. Native 4K content need not be streamed with its obscene bandwidth requirement. For those few people that do manage to maintain a 4K stream, I suspect many will consider it a nice perk or bonus, especially given how poorly compressed the images via Netflix are right now.
The BDA may very well get behind BD4K. But I suspect it's likely going to be for more commercial/industrial use of data storage than consumer. Sure, someone out there will make players for the niche market. Sony may even make the discs for the consumer to buy. But I'm not holding my breath that either will be available before 5 years have gone by, and even then I'm not convinced that any sort of disc delivery of 4K will ever become affordable.