This alternate universe would be amazing to play around in. Enormous living creatures being ridden into battle by fantasy warriors to fight in giant MMO wars. This is a parallel reality we want to see happen.
It would be a reality where scientists have genetically designed new breeds of dinosaurs and dragons, allowing players to equip these terrifying mounts with all sorts of mechanical and military add-ons -- lasers, shields, turrets, sensors, and more. And as player's progress to higher tiers, modifications and gear sets would become more diverse and powerful.
Of course, dragons can be divided between different fighting nations or factions. Players could also choose different types of dragons. Smaller and more agile beasts would operate like some sort of light tank or light aircraft. Bigger and heavier dragons, equipped with rocket launchers or high beams, long distance lasers, and more would be like B52 Flying Fortresses or Tiger tanks.
Perhaps riders could even be grouped as crews – small dragons would require only one crew member but huge ones would need full crews to operate.
It seems that this could give players endless options to choose gameplay styles, resulting in hours of fiery battles in the air above.