|A 4K splitter sounds like a good idea for making it future proof.|
However, I'm not aware of any DVR that outputs in 4K because nothing is broadcast in that yet. You can get 4K on some streaming services like Netflix, but I believe you have to use a streaming box for that such as a Roku or your 4K TV.
Please correct me if I'm wrong about that.
I believe 4K broadcast TV is coming, but I'm only aware of it being available over-the-air (OTA). The bandwidth required for 4K is substantial, so it'll be years before it's available on cable or satellite.