Seems realistic to me as well. I love the IS and love to drive ours, so it seems to me like Lexus is going to build upon the car's existing strengths with a few modernizing tweaks, which also just so happens to be very cost effective.
The platform still feels great to me, so the news of a carryover platform doesn't bother me. The only sore spot here IMO is the engines - we need a new ~280hp ~35mpg turbo 4, and a 380-400hp turbo 6 just to remain in the same ballpark as Audi, BMW and Mercedes. While all of this is great for Lexus fans and IS loyalists... I ask myself many more of those exist in this market. Buying a sedan is increasingly becoming a lifestyle statement, or done by those who truly enjoy driving, so the models that remain are fighting for a smaller portion of buyers, and the lack of engine updates is going to be a big problem, IMO, both for power and MPG.
I also worry that this is the coming end of the IS as we know it, and Lexus is likely winding down the program. We've seen them make similar moves with other models where they do just enough to make it passable, then ultimately terminate it. So many years later, plenty of new engines and new RWD platforms, and the IS gets none of that? Not a good sign. I posted a lot of this earlier in this thread and was told by someone at Lexus that the company now sees the IS as a niche model and not worthy of significant investment.