I actually do not think it is the Sims 5 myself - or if it is it is for that S.E.E.D. program which should be in the works in the next 4-5 years. That program is said to use the Frostbyte 3 engine - EA's inhouse game engine so that could account for no new engine contractors. I know for a fact this program is EA's baby and they have been working on it quite a long while.
I see Sims 4 going beyond the 3 years myself - personally just from the way the future games are discussed at the quarterly meetings and the determination to get the new system brought to life. Granted I don't know this for a fact - but Andrew Wilson made it pretty clear it is the future of gaming and not just EA's future.
