I've always wondered why this was. Yes, I guess the Telvanni wizard and Redoran samurai-ish cultures might be a tad more interesting, but that's not to say that House Hlaalu is boring. The faction questline has quite a bit of intrigue that would be interesting to explore further, especially the paradoxical alliance House Hlaalu (technically the most imperial-friendly house) has with the Camonna Tong. Basically, there's tons of potential for a faction expansion mod that I'm seeing, which no one has exploited.
I've done some digging on cyberspace and found two mods that appeared to fill this void. Theres Grandmaster of Hlaalu by Lady Galadriel. However, the current release has quite a few bugs and, while her last forum posts said she was working on a 1.3 update, I can't tell whether that's still in progress. Then I heard a "rumor" about a so-called "PAX Hlaalu" mod, but haven't been able to find out anything about it. Is the mod buggy? Will it crash my game?? Without any description/readme, I've been afraid to see what it does.
Anyways, with law school on my plate I probably won't be able to work on a project this ambitious. However, I was wondering whether anyone else might be working on a mod like this, or also had some great ideas for such a mod. Awhile back, I started work with a friend on a mod to make the confrontation with Orvas Dren more interesting and challenging, that I thought about taking in the direction of a faction-expansion, but then law school started