I almost never support the removal of things from the game. I include Naxx40 in that list and I have a whole set from back in the day. I think removal of things is just bad unless it is released with a ‘temporary’ status such as Mage Tower from Legion. It was never in doubt that it was there for that expansion only.
The above said, I think this mount was only ever designed for the AH mogul. They wanted them to be able to do AH things while also out in the world so they were not stuck in town. These people would spend hours and hours in town doing nothing but monitoring the AH. The removal of the mount to me indicates they might even go away from the mobile AH altogether. The reforge mount was changed and became a transmog mount. It is very possible Blizzard does not like the mobile AH and could change it into another transmog mount or something entirely different. If you can afford it and you worry about missing out on things then grab it but their removal of said mount is likely to mean they did not want people with its function and in the future it will probably be changed.