I believe the reason KLM is moving to this is maybe to indirectly get more €€/$$ for those Eco+ seats - most probably due to after years of trying to sell them, not getting sufficient traction.

But yes I do see this indeed as penalizing FB Elite members especially FB Gold who currently can only select these seats complimentary 36 hours before departure. A very bold move in my opinion from KLM's side - but I am sure they must have done their homework and with this, they know pax are going in any case now want to pay for it or just hope pax will get "tricked" by seeing the Eco+ wording in the option as a reason to upfare for a reasonable value.

Sadly, I see moving forward more and more of such "customization" to force pax to pay even as a loyal member within the program.

Cheers!