A couple more possibilities to add into the melting pot in regards to some kind of diorama.
First off is a Warhammer Quest dungeon scene, but using modern models. A bit like the one Mike McVey did years back where the whole thing is split into a number of micro-dioramas with different monsters and party members. For the barbarian I think it would be possible to convert a Chaos Knight into a much more ‘Conan’ style character, Wizard would be the new empire wizard box, Elf could be one of the wood elf range and Dwarf could be converted from any number of Dwarf models.
Whilst searching (the wonders of Google Images) I also came across a number of pretty cool Tomb King landscapes (mostly from Warhammer Online), which would make a quite refreshing backdrop to a diorama as it would use light sandy colours and rich Turquoise and gold’s, plus you could create some pretty cool ‘sand effects’ with things bursting out of the sand 😀