I was going to post an update when I had a bit more info. However, since you ask, the latest position is:
Disk life is highly dependant on usage. Many reports of 100K miles plus for normal road usage, but just as many reports of very low mileage for heavy (read "track") usage and quite a few reports of poor life with claimed gentle use. Of course my definition of "gentle" and yours may be quite different. (reports based mainly on 911's). I have had a chat with a local Porsche specialist and his view is that the Porsche Centre may be "erring on the side of caution" He has measured all the disks and thinks they have plenty of life in them yet - time will tell.
Options:
1. I haven't yet found any aftermarket ceramic disks - still looking.
2. JZM will refurbish disks for less than £10K. Downside is that they need them for 30 days which doesn't work for me as the car is my daily drive. They do offer an exchange service if they have them in stock. Probably works for the more common 911 variants but probably not for a 970.
3. Steel replacements are readily available from the US from around £5k. Makes such as Brembo claim significant improvement over Porsche standard steel brakes.
4. I may have found a UK source for steel replacements for nearer £2.5k but need some further details.
I'll post a further update in due course, but unless I find a more economic ceramic option I will switch back to steel disks.
Hope this is of interest.
Graham.