Will there be an option for 4k?
It is targeting mostly people which have a slow connection but some may also have a good connection too.
I think so but probably not for all the content. YourDef is a good idea. You don't need 4k streams on a phone.
Have a look into the whitepaper. There is the posibility of flexible resolution. For examble a mobile device got a lower quality than a TV on streaming.