Generically, the limitation with current 4K TVs is exactly about the input rate, not about the display rate after that.
The quality of up-conversion is the next issue with the likes of the Seikis, compared to the major brands that are charging 4-5 times as much. As I have said, if the Seikis will at least work as reasonable monitors for Cubase and general computing (but not necessarily TVs or video editing)
Sorry, what do you mean by ‘output combining’ as it relates to current and future 4K TVs?
When I said about multiple video cards, I was referring to CrossfireX (AMD) and SLI (NVidia) links to combine the GPU power to go out one high bandwidth video port, like DisplayPort or DL-DVI. Most of the power is about getting high framerates for gaming/video, because only one card will handle Cubase non-video stuff at 4K.