When the PC version comes out I think we will have more Mod discussion as we have far more control over the IP. It is a major component to PC gaming and BW has been a big supporter in the past of talented Modders (we even hired some to work here).
We won't be releasing a kit as far as I know but if there is interest I'm sure we can figure out ways to support a modding community.
I would imagine mission creation would be tops for the skilled. I imagine after the experience of NWN we will see some quick reskins of the armor/weapons and then work our way up to seeing new levels and missions.
It will be very cool to see what people come up with.
It'll be very interesting if they do support modding; while they won't be releasing a toolset, it is possible to mod without one--just difficult. I for one would like to see a Tali or a Garrus romance!