Well "Underfoot" very much ties in with EverQuest lore as the home of Brell, creator god of the Halflings, Dwarves, Gnomes, Gnolls & several other races.

Access to the "Plane of Underfoot" was mentioned several times in the Lore connected to "The Hole".

Sounds interesting, I quit EQ because SoD was such a pile of crap expansion (as far as I am concerned) , I'd be tempted to check out an Underfoot themed expansion but it would sure as hell need more going for it than SoD had, perhaps with Free Realms doing so incredibly well SoE can invest a little in (or not suck out of) EQ this year & do something decent.