I like the Idea. Reading the Title of the Tardis Doors with those cute ponys looking forward made me just smile.
This is so cute.
The drawing of the Tardis could be a bit better though. So that it would fit the stylish background better. I can't say if that would be enough, since the pony's are drawn like comics. Or maybe it would be better to exchange the background by a more comic-like background. So you would only have to rearange the background.
Of course this depends on what kind of picture you prefer to achieve.
This is really funny though and leaves me with a little wink in the eye