Here's some things I think would be good for such a supplement.
Anything like B Hanson has posted.
NPCs
Locations, such as small villages, hamlets or single shops (perhaps some in Sel-kai)
Short, one page adventures
New magical items, particularly those with a definite SW association (although perhaps not extremely powerful ones like Orbs of World Rending)
Unfortunately, I can't see us charging for material that Brian has already put up for free (just like I would not charge for the Grand Campaign or my Towers PDF). But there could be new and interesting custom spell lists.
I also like the idea of a shop, with an interesting owner NPC, maybe in Sel-kai but could be dropped elsewhere.
Or an isolated inn along a highway, where all kinds of things could happen. (
Green Gryphon was originally supposed to be a small adventure like that and it kind of got out of hand)
And yes, Items should be more minor but unique things.
Nicholas seems to like the idea, but not a subscription. We'll need to see if we can com up with enough material...