M4 GTS price = 2 x M4 price = 700 cars = sold out.
http://www.evo.co.uk/bmw/m4-gts
M2 GTS price = 2 x M2 price = limited quantity = will be sold out.
Plenty of folks with deep pockets who want to add a low production halo car to their stable of exotics.
However, I believe that there will be no M2 GTS in the near future. M2 CS is rumored to be the first M2 variant to be expected (MY 2018), if BMW doesn't change its mind.