What lies beneath the surface of Kaelaross? Right now I'm not too sure. I certainly like the idea of vast subterranean realms of lightless caverns, passages and fissures. However, I am wary about one important thing - AD&D underdark races.
In my opinion they are all rather over-used. I don't think this is the fault of any designers who first came up with them (at the time they were all very cool), but I think subsequent designers have been increasingly lazy in not bothering to look beyond them. If I did create an Underdark realm for Kaelaross, I would want it to be as original as I could make it.
Races that I would avoid include:
I guess one of the things I've wanted to do with Kaelaross is keep it Basic/Expert D&D, not Advanced D&D. Not everyone will agree with me on this, and I'm sure lots of people have had great adventures going through the underground realms of Greyhawk (the D1-3 series) and the Forgotten Realms (Menzoberranzan), and many who still do enjoy these staples of AD&D. I do not want to detract from their enjoyment, and I don't intend to put down any of those creations.
Nontheless, I do want to make a fresh start - If a DM or a game designer who knew and played Basic & Expert D&D but had not encountered AD&D (especially existing material on the Underdark) was asked to think about a kingdom-spanning network of caves, caverns, passageways, sinkholes and underground lakes, what would he do?
Right now I'm not sure, but I hope it's going to be good. The one thing I am concerned about is getting over-ambitious and finding I've bitten off more than I can chew. I imagine the underdark to be an extention to Kaelaross rather than an entire setting in itself, but it is potentially so vast I could get lost in it. And if you haven't seen an idea for a campaign setting that turned out too big for yours truly to handle, I point to my previous attempt at a blog which I have given up on.