I am not sure what this policy change has done, but recently even on a B-subclass Eco fare, as FB Plat, I was not able to select Y+ and not even on the upgrade list (although was listed on the upgrade list for First).
On the day of travel, at the counter after asking about it, they managed to add me to the upgrade list, but all the way to the back of a waiting list of 32 other DL FF ahead of me

I am not sure if KL still offers DL top tier elite members complimentary selection of the Y+ seats on both EU and non-EU flights, if they do, it seems that there's some unbalanced reciprocal agreements.
I am going to after my trip write a complain to FB Customer support. Previously as a Plat, Y+ seats were offered complimentary on both KL and DL without issues.

Cheers!