Morning, mate! The mega bundle is something I have been considering for a while, but from what I have seem so far people favour more charsets than tilesets.
I do plan on expanding the theming of the tilesets as well as the regions. However, since it get so much less traction than the charsets it ends up on the backburner.
For the next expansion I am planning tackling snow/ice, so snowy city, frozen wastelands and icy cave. But I have no timetable for that one :(