Quitting Sims 3 means I would have to abandon my family with which I´m playing since the day Supernatural came out.
So, if I can´t replace this big and beloved family exactly one to one to the new Sims 5 I would not move on. (Perhaps the new game would/could be able through body and face scanners of pictures to recreate them?)
And there are other features the game must have: Open Worlds (bigger and better than the ones in 3), CAS (even better and faster and more customizable) and a Story Progression like Nrass´s.
And the Sims have to react much more to the other Sims and their actions and behavior. They should have sympathy and empathy to their fellow sims! And the families should have a much bigger bond than in the former games. This new Sims should behave like little humans somehow.
And Sims 5 has to be graphically improved to Sims 3. I want more realism! Forget about this (sorry to say my opinion) shitty awful comical graphical style of Sims 4. I don´t want to have the feeling again, that the developers have made a bad joke at the expense of the Sims!
If all this improvements were taken into account while making Sims 5, I would move on. But I doubt that EA and Maxis would put so much effort to the Sims 5, it will be too expensive and too much hard work!
