I would very surprised if any of the following does not happen:
(1) ISF marginally faster than M3 in a straight line
(2) M3 faster than ISF on the track
(3) ISF cheaper than M3
(4) ISF offering more interior luxury than M3
To take any of the BMW-M market Lexus has to offer a car at a price that might even be losing them money in the first year. They did this back in the very early 1990's in a different category with the introduction of the Lexus LS400. As soon as the car became a "hit" they raised prices.
They won't take the "enthusiasts" and "fanboys" from the BMW brand but that part of the market is probably low single digits. I sure plan on checking out both cars when they come out. The more choices the better.