I think there will be a physical PS5/XB2 ... but it will also start to become optional by next gen whether or not you want to own hardware or not.
There won't be a PS6/XB3/NX3 or whatever, upgradable or not because 1 gigabit internet will be standard by then and games will be able to be streamed even in 4K+ resolution.
If Netflix decides for example to offer a gaming service where you can buy whatever game you want, but you don't have to pay $400 for the hardware, and you can run games on high effects that evolve over time ... the Sony/Nintendo/MS model is going to look really, really badly outdated, but Sony is already test driving this idea with PS Now.
Really ?, 1GBs Internet ?, where i live you need a Internet of 5GBs, to get a 500MBs, PS5, would launch in 2019-2020, PS6, 2025-2026, i don't think that in 10 Years the World will have such Internet, maybe in Korea.
Korea's Average Internet Speed, is 21.0Mbit/s, is the Faster internet in the World, the seccond best internet is the Japanese internet connection, and is 12,9Mbit/s, USA, Average is 10.00Mbit/s.
The World's Average is 3.84Mbit/s, how the Average will became 100 Times better for USA, and 250-300 Times Better Worldwide, in just 10 Years ?.