I am wondering if, at 70", you will notice the difference between 1080p and 2160p. I am going to honestly say that I think the difference will be negligible.
Keep in mind that the difference between SD and Full HD is staggering because there are 6.75x more pixels. It's night and day. There's a lot of support for HD content, with movies, TV, sports, and video games all supporting it. That said, 1080p for TV content is still not possible, so there is still a lag in content delivery.
However, the difference between 1080p and Ultra HD is not as large.
From personal experience, I can tell you that the difference between even 720p and 1080p isn't very noticeable until you go into very large screens.
I think the markets have accepted Full HD (but not 3D) and will stay there for a while.