@q : not as classic as javacrpg (why did that die btw? Legends of Grimrock is such a great game, even though frustratingly hard at the end), but yes DH was one of the few projects that attempted it.
LoS is not really contender since it seems to me to be based too much on dungeon mining and exploring (after all that is the key feature of the engine). However if the GUI system was enhanced and outdoor rendering focused on, it might be a good engine to start such a project.
About the comments that it is too much work... well that applies to single-player games in general. One could go the Never Winters Nights approach though and make it very easy to do custom story-lines to "crowd source" the story content.
About the too much content comments... well yes, but surprisingly enough there is A LOT of high quality stuff done already. I recently browsed through the OGA database while thinking about what could be used for the content pack of OpenMW, and it struck me that for such kind of RPGs there is really almost everything there already (great high quality 3D fantasy characters, an almost unlimited amount of medival style weapons and furniture, great plants and other vegetation, some good enemy creatures, and last but not least really great 2D menu/GUI artworks for inventory graphics and spells etc.).
It's a pity really that those are hardly used it seems... and for the existing top down RPGs or for other game genres those assets seem to be mostly not suitable.
Edit: Well a quick idea... maybe one could do a fantasy Left 4 Dead kind of game with light RPG elements. One dwarf, one elf, one barbarian and a wizard (e.g. the archetypical D&D group) band together to co-op explore dungeons. Would be more FPS like, most likely, but that would a game I would enjoy playing (as opposed to Skyrim or Morrowind)
