Exactly!

PS4 is a loooooooong way away, market could be very different at that time

Yeah, but will Sony still be in the gaming industry to see it? I have my doubts, if the PS4 is such a long way away. They need to admit their mistakes, learn from them, and start anew, and they need to do it much sooner than they probably will.

The best thing Sony can do is ride the PS3 out as long as they possibly can. They have already lost all of the profits of the PS1 and PS2 on this system so it would only make sense to wait until your profitable. Then when the PS4 does come out, try and not be fools like this gen. We don't need everything under the hood that is possible. Make it advanced enough that it can compete with the Wii2 and the Next box but don't over due it. Then they should do well as long as they try and stay humble.

Next Generation they will have more and better Systemsellers

Like Killzone 3,Uncharted 3, LittleBigPlanet 2 and so on
That´was their problem this generation no games the first year and a high price tag

If they allow the next Xbox a year, or even a two year headstart, at this point, with our limited information, Microsoft would dominate the market. We saw what one year did.

They could just improve the RAM, GPU, and make some sort of hybrid CPU to make the PS4.

The hybrid CPU could be something like a Cell with multiple PPE's, so it would be competitive with the Xbox's CPU on direct ports and still have the additional abilities of the SPE's on top of that both for exclusives and ports that choose to use it. Ports don't have to be so much better on one console to blow the other away to be successful, they just have to be undeniably better, even if the difference is minimal.

Why would Microsoft make X720? The other two consoles will have online...

See how illogical that reasoning is?

Sony shouldn't make a ps4, four is a bad luck number... Sony should call its next console something else and try to recreate their image while not alienating their current fanbase.

The question from the OP should include a time frame.

Release it sometime in the future, of course. Anytime in the next 5 years, I think they won't, and will do right.