It would pretty much have to be 4K compatible at that time. So...
3.6 GHz 8 core i7 CPU (2 cores dedicated for OS).
GPU equivalent to 2015 second highest level graphics card.
16 GB of unified DDR5 RAM (4GB reserve for system).
No disc drive models (cheaper models without disc drive, and premium models with).
64 GB unremoveable SSD (for system OS) and 3 TB upgradeable HDD (5 TB on model with no disc drive).
Overall, I think they follow the same gameplan as this gen- release relatively mid-range specs that just meet the resolution requirement for a lower price than normal (expect around $400-500 again).
You're Gonna Carry That Weight.
Xbox One - PS4 - Wii U - PC