I've said this in a previous thread about the subject and my feelings haven't really changed.
If Renault and Kubica want to work together and they both feel he'd do a good job, then go for it. Even if it was a one year deal I'm certain he would get an amazing reception at every Grand Prix.
The problem I feel is what does Robert want out of the deal? Does he want an F1 drive that will delivery wins? Podiums? Lots of points? I'm afraid to say I think Renault are still a few years away from regular podiums and I just can't see them winning in the hybrid era. Mercedes and Ferrari are just too far ahead.
It's just a feeling I have after the few other tests he did that he has no desire to finish 12th or 14th, he wants to win races. If that's his desire I think his best option is either something like WEC/Sportscar or even the '18 spec Indycar where I'm sure he would be very welcome. Depends on whether he's an oval fan or not.
In reference to the post about F1 cars being easy. Well done on doing a good job and I'm glad for you that you did well. However being in F1 is a lot more than just driving the car. It's politics, it's dealing with nastiness, it's dealing with pressure from the team, pressure from the media, pressure from trying to raise the funds 24/7, a dozen media events every day, and spending most of the week in planes flying from one venue to another. Also don't forget there are only a few F1 drivers that are actually paid, the rest just survive the best they can.