Only Forgemasters of Thurgadin has a merchant yet, but since quests reward this faction already I'm suspecting there are plans to add a merchant soon (tm).
There is an othmir quartermaster, Flynn, near where Misa is, standing right at the bank and broker. But all he/she(?) has is jewelry and adornments for othmir faction. I saw nothing else like house items or such.
I was also wondering if a daily Othmir Artisan Task NPC was somewhere.. but until there is a merchant which sells items based off the faction, guess it doesn't matter.
