The 3.3L (as in RX330, for one example) is a V6 configuration; the IS uses the I6 from the (short-lived) GS & SC300 models. So the more likely scenario is that ToyMoCo will keep that block the same and instead add variable valve lift/duration to the variable valve timing (a la the Celica's screaming 1.8L I4). That should get you 10-15% more ponies.