We have some plans to try to expand out the game, but its more or less a question of time. A fair amount of my personal time is going towards setting up the new site. After getting it up and running we may have the time to look back at this.
One idea we where actually playing with but did not get time to implement is the dragon would break through the floor as they got larger and open up a new randomly generated level.
As for out of bounds, no nothing hidden. I think I have a wall set at the edges that can not be dug up.
I still thinking about some upgrades and expansions, like adding that dragon's face on that timer bar thing and countdowns till summoning you back to them