But: As I had no EN-GB Pro installed, I installed now when Gabe Aul tweeted about release of 11099 an EN-GB 11082 on a virtual machine, activated it, set it on fast ring and rebooted. It immediately picked up the 11099 upgrade and I have already created the ISO image.
Short: an existing EN-US Pro 11082, no upgrade yet. A fresh EN-GB Pro 11082, installed an hour and a half ago, already upgraded to 11099 and ISO file created.
EDIT: With the exception of Jeff, all the other posters here who are up on 11099 are OUTSIDE the US.....
Apparently very random thing.