Tesla will NOT use the same motor as in the S and X.
Why would they? The Model 3 will be 20% lighter than the S, so a smaller motor will give plenty of go power along with the required efficiency.
There is also a report of a third party vendor stating they are making permanent magnet motors for the M3. SO if true this will be a major departure for Tesla. But one thing for sure is that Tesla is not afraid to challenge the current orthodoxy...even when it is their own.
Some think they will be using a new, hybrid type motor than is more efficient than a given induction or PM motor of the same size.
This is the fun stuff we get to see at the next reveal.