Beyond the issue with unsprung weight, that seems like a truly awful trade-off. A run-flat still needs to be serviced if punctured and is still vulnerable to sidewall damage and potential blow-outs. If you carry a full size spare (I sure do) in the event of most tire failures, you still have the ability to get much further down the road with less drama.
None of the new sedan vehicles carry a full sized tire, they all carry a temporary one, which can only be driven 50 miles at low speed. So still worse than broken run flat
They don't come with one stock, sure, but there's nothing to stop you from going and buying the correct sized steel (or cheapo alloy) wheel and a decent tire that's the same size as the ones on the car and carrying it with you (and throwing the junky temporary spare out). Yeah it requires you to work a touch extra on the setup, but it is worth it. The extra full size spare will cost about the same as going with run flats vs non-run flats each time you swap out tires.
If you're interested, it's pretty easy to get the correct sized wheel from somewhere like RockAuto or Discount Tire Direct.
I have a 5 series bmw (f10 latest one), and I have had other premium cars before and I (and many car experts) can tell you nothing comes close in this price range in terms of handling and comfort of BMW, run flat tires make no difference for me compared to regular tires on my previous Merc and my friend's audi a6.
Why downvoting? It's my personal experience and opinion? Sometimes I don't understand HN users...
I didn't downvote you, but I'd guess the reason was that you brought an irrelevant fact to a discussion about run-flat vs regular tires - it doesn't really matter if a BMW with run-flat still has better handling than an Audi with regulars.
