On Dmitry Krupski’s website there is an interview with Michael Guthmann (Product Manager PEN & OM-D, Olympus of Europe) where the following is stated:
Translated: We are carefully studying this point. While we do not think that for the target audience E-M5 II 4K mode is necessary. So we are closely watching the market – perhaps in future models 4K video will be realized. While I can not say with certainty whether the 4K in a model that will replace the E-M1.
Yes, we understand that other manufacturers – Panasonic, Sony, Samsung – offering 4K mode, even in top-level models do not. They just need to create content for their TV. They need to sell 4K TVs. While the content in 4K very little, so they want to have on the market as much as possible models that can shoot in 4K. But we do not see great potential for 4K at the moment. Once the market is ready for it, we will make 4K.