Lot of people say that next sony console wont be running at 4k, but I think it will.

If you look at current high end GPUS, they can run 4k average games at high settings (not ultra with MSAA, but high). Next AMD Nano will be faster than R9 290X. So It will run games at 4k medium settings. 

At the time of lauch, PS4 run like a HD 7850 mid range card. And that is like the best GPU from 2009-2010. A
HD 7850 allows games at 1080p 30 fps medium-high settings. A littel behind a R9 270X. Same thing with PS4. Runs games at 1080p medium PC settings. 

The thing is, if sony makes a console in 2018-2019, they will be able to put AMD Nano performance (2015 - 175W) into a PS5 (2019-100W). So it will be able to run games at 4k 30 fps medium settings. (with current games quality).

There is a lot of stuff that will add performance. HMB memory, shirks to 16 or 14 nm, faster designs. So, they can make it to 4k.

It needs but I don't know :(

Considering that current consoles are mainly custom PC's and that the Fury X Pro is a stellar card, it isn't entirely out of the question. Still though, who knows? We still don't know how long Sony or Microsoft will continue support for either the PS4 and Xbox One.

At steady 25fps.

How many people have 4k TVs? They won't have the PS5 output at a resolution that the majority of their customers can't use

Logic tells me that after going to x86 there is no going back. I mean, Games will be compatible, they perfectly can make games to run at 4k in a PS5 and run 1080p in PS4. Like apple selling Iphone 6 for hardcore and old Iphone 5 to buyers that look for cheaper stuff running the same IOS. Or like running games on a PC, if you have the best graphic card you can run 4k, but if you have a mid range one you can run full hd.
I think PS4 will be a "mid range card" and PS5 the high end one that will last longer.

I would be happy with a PS5 running at 1440P but with everything else graphically maxed out ( Textures etc. ) and running at a stable 60 FPS for most games. 4K television screens just aren't going to be a thing for a while and next gen consoles can do without outputting their games at that resolution.

Meh, we will see...

i rather have 1080 - 60 and all the extra power used to make more technically demanding games and therefore more impressive games gameplay wise. (like imagine a GTA were you can actually enter every single house, apartment and building in the city and imagine it having destruction a la battlefield bad company 2 (or better than battlefield bc2) thats just an idea of stuff they could do with the extra power, not everything needs to be graphics.

A lot of 4k TVs are being sold. In 4 years a lot of TVs will be 4k, just as PS3 run at HD or 1080i and after 7 years PS4 runs 1080p. They will go for 4k. Some people (almost blind I guess) say that the graphic difference between PS3 and PS4 is not much. If they dont make PS5 a 4k console, It will be hard to justify the money spent.