Why would it be costly?

To answer your question Maf, yes. Being able to play with the controller and eventually introducing the game to consoles.

What would make the downloadable client even better (for Tanki and TankiX) would be to make them have the ability to interface with Xbox, and/or PS4 console controllers. This would provide a whole new aspect of the game, including being able to transfer the game all together onto consoles. It has been done for hundreds of other games such as Fortnite and World of Tanks.