A few years ago AF decided to go hand in hand with 2H and drop its CDG-BRU flights in favor of ZYR-CDG high-speed trains. Check-in (or so) is offered at ZYR but you still have to transfer your luggage yourself at CDG and hence line up in the queues there.
Now AF has acquired KL and a similar option could be envisaged to replace KL's AMS-BRU flights with a ZYR-AMS (maybe pending the inauguration of a shorter travel time between the two stations which currently stands at 2h40 compared to 1h15 on ZYR-CDG). AF's existing agreement with 2H may make the thing easier for a deal with its KL part.
Imagine AF and KL both having a high-speed train link between ZYR and their respective home airports, providing countless connections to their network and eventually sharing that advantage with their SkyTeam partners. You could see a CO, DL, KE, MEA, NW tag on any of these train services (alongside AF & KL) that would boost those airlines' offer and visibility on the market but could be a serious blow to the airport's ambitions, whichever they may be.
SN has recently inaugurated its high-speed train service between BRU and XPG to cater for Africans in the Paris area but this offer is in no way a threat to CDG compared to what the above fiction would mean for BRU.
I believe that this is a unique situation in the world today. Do you think it is normal that a specific carrier/alliance be given such a competitive edge over the local airport and its operators?