Hitmonlee and Hitmonchan
The most obvious absence from Pokken Tournament DX comes in the form of fighting-type Pokemon Hitmonlee and Hitmonchan. Each named after popular martial artists and generally just cool-looking, it seems like a no-brainer for Bandai Namco to introduce these two into the game later on with a patch or as DLC.
Hitmonlee could have powerful kicking attacks like mega kick, high jump kick, and blaze kick, but that could leave his upper half exposed and weak to charges and/or projectiles. Hitmonchan, on the other hand, could have powerful punching attacks like mega punch, focus punch, and close combat, but his lower half could lack in defensive capabilities.