Performance is going to make the past generations look silly. IRS, an increase in power, a decrease in weight and dimension= killer track times. I think this car is going to be a huge hit. I'm glad they are moving past the retro look, I was sick of it in 2007.
For the most part, this is basically the case with almost any long-running car. As much attention as the original Falcon-based classic Mustangs get, stock for stock they are totally obsolete when compared to the S197s. For all intents and purposes, I wouldn't doubt the S550's successor will outperform it too, as time marches on technology improves this is basically the only likely outcome.
I don't think the S550 has ditched everything retro, the lines are still very similar to the S197 IMO, the tri tailights are still there, and the fascia is essentially almost the current one with new style headlights.