2020 would be perfect in my opinion, so around 4 1/2 years until PS5 will be in my Hands.^^

Yes, since I dont have to upgrade or buy new hardware :p

2018-19 is when it should end.

Well I'm a play mostly on PC, so generations are a but nebulous for me.
I know people complain that the current consoles are woefully underpowered, so I guess it'd be nice if we got new machines. But you just know that if Sony and MS put out new consoles and say to developers "Now you can get your games running at 60fps!" the developers will immediately push the graphics up all the way and be like "what about 60?"

honestly makes no difference to me. I was still ok with the PS3 by the time the PS4 came along. Just give me the games.

Definitely a long generation. I want big third party developers to put out 2 - 3 major projects, same with first parties.

This gen will prepare pioneer VR device, apps and games, but to make the most of its potential, consoles will need high HW power, and what's more, they'll havce to offer high power and VR device at an affordable price, so if next gen will launch too early, it won't be able to do it and mainstrem VR will have to wait for 10th gen, but this could open consoles to the risk of disruption by mobile derived devices. This could happen even to 9th gen, if it were too late, so careful timing will be of the essence, 9th gen must not launch until it can offer high computing power and a VR device at a good price, but once this is possible it must launch quickly.
So I'd say 2019 or 2020.