Tartarus is an icy inferno.

As I said, the idea is good, but I don't like the fact that you want to replace the Necropolis...

Hehe, they'll replace it with another Castle, and then other people won't like it... you can't cater to everyone.

Although, it would be better to replace the Conflux (and do this in all cases with new Castles), because the Castle is the least interesting, and it only appeared at the end (and replace it, if the Castle will be in SoDe and other expansions where the Conflux exists). IMHO.
P.S. In general, forget about the Conflux!