[noggin]

I think studios & manufacturers are waiting to see how 4K BD's fare/sell before introducing 3D 4K... getting most to re-buy movies in 4K is already a hard sell. From DVD to Blu-ray, most could appreciate the difference, but it's the law of diminishing returns for many from 1080p BD to 4K BD. Honesty, you need a 65" or larger display at least & need to be pretty picky about PQ (us lot) to appreciate & be willing to pay for. I see 4K being nothing but a niche format.

its like you mentioned with 3D, its a personal preference thing i guess, i have a 55" UHD 3D LG Display and watching Exodus or Life of PI Bluray vs watching the HDR 4K samples floating around is like night and day difference, to me at least. Netflix UHD and the likes just dont do the format justice. i also love 3D and find the experience at home to be much better than at the theatre, passive 3D glasses are very comfortable and mine all weigh much less than most expensive sunglasses.

If you're watching a 3D Passive UHD set then you have a maximum 1080p vertically as the limiting factor is the display - as you only get alternate lines in each eye with passive 3D (Passive 1080p displays only gave you 540p). So you would get 3840x1080 resolution maximum with a UHD 3D format. You'd either need an 8K Passive UHD2 display, or a flickering active display with LCD shuttered glasses, to get full 2160p vertical resolution. I suspect this is another reason 3D UHD may not be at the forefront of the standard.

It may also be that 3D Blu-ray hasn't set the market on-fire, so two 3D Blu-ray formats may be a bit too niche...