This game is designed for 9-tiles. It won't run well if you unlock more tiles without a ton of mods that will bog down the game.
The devs aren't going to unlock modding. there is already a case of hackers attacking users recently from the Steam workshop.
Consoles won't allow it either, they don't want their system to be hacked.
If you want it badly, keep pestering Microsoft/Tantulas and have them fully implement mods.