I'm guessing they might carry a serious cost and weight penalty?

I never liked the runflats because of the stiffer sidewall. Yes, I had PSS runflats on my Vette and they were probably the best of the runflats for the Vette, certainly better than the original GY. I think there is an amazing difference in handling between the non-rf and the rf.
Larry

Lance, there's not much of a cost difference, about $200 more for a set. I don't think there's much of a weight penalty either, maybe 1-2 lbs. per tire. My C7 rides much nicer than my base F-Type, but it's a confounded experiment because the C7 has magnetic selective ride control.

Runflats have come a long way in the last 5-10 years. However, I did put a set of Michelin PS AS3+ non-runflat, all seasons on the car because I'm driving it all winter, and the PSS starts getting very slippery below 50ºF. They do ride a bit softer. I'll put the PSS set back on in May.

Larry, those who have tested both versions of the PSS on the C7 did not show a detectable difference in performance. They have exactly the same tread pattern and rubber compound. I had some real numbers somewhere, but can't lay my eyeballs on them right now.

Nice! I wish the F-Type offered that.