Can you tell me if it's a good ideaFollow

Perhaps as free downloads since SOE doesn't release expansions that require other expansions to access the main content. You might see PoP quests that require a trip to Kunark but you don't see an expansion only accessable from Kunark, for example. But, as Veksar shows, free content is exempt.

Even in the old world, I'd like seeing a gnoll oriented LDoN theme in S. Karana and a kobold oriented one on Odus. The Warrens, according to the game lore, are part of the remains of the original kobold city dating back before the elves, dwarves and actually any Norrathian race except Veeshan's children on Velious. Finding the deeper ruins of city would make an appropriate and interesting LDoN theme (or even just a dungeon zone).

Personally, I always wanted to see a Stonehive LDoN theme full of bixies but I get no love from anyone on the idea

Out of the ones I mentioned, S. Karana is the only one that'd really be made easier. Toxxulia forest has two PoP books, a Nexus/Wizard spire and a druid ring in it as it is. I don't think a Wayfarer camp would break it

If you take the Stonehive thing seriously, W. Commons would be a good place for the zone-in since Misty Thicket would be a bit cramped with a camp and Kithicor Forest has the obvious issues. For W. Commons you could almost just throw another couple NPCs in the EC tunnel if you wanted. After the spell merchants, tome merchants and Wayfarer camp, what's a couple more NPCs? I wonder if the Shady Swashbuckler ever misses the times back when it was just him and Bubar.