Never ever? 
I read that they would be available next summer.
Though that was a few months ago and could have changed.
Part of the email.
What’s happening with Pilot Sport 4S?
Well in Europe the tyre is sold in 19” plus sizes, with only some limited production of 18” (in Michelin Factories in the USA) being made and sold only in their market
We make 19” plus sizes in Europe, and predominantly for cars with 250-300bhp+
Why? Well the performance difference in 18” is seriously small (PS4 vs PS4S), unlike the old difference between Pilot Sport 3 and Pilot Super Sport (which was a major difference)
Hence the production in the US factories, will stay in the USA. Every time we import and approve a tyre for sale in Europe, you can imagine there is some cost.