Cormyr as the aggressor in a war with the Dalelands - doesn't feel right for me, but it could work as a good idea for some political infighting in a Cormyr that is still trying to find it's feet after the war with the Netheril, and some factions/nobles might not be as defensive/passive as the...
I like the Sembia angle, though I would suppose that a lot of the Netheril (or whatever is left of their forces) would have moved towards the Farsea swamp, where I believe they had a staging area for their invasion, and from there North towards the desert assuming there is anything to return to...
I'm in the process of putting together a campaign for the first time in a very, very long time, and I'm thinking of taking my friends back to good old Cormyr, with a base (at least in the beginning) in Arabel.
Many years ago (in real life) we played AD&D in Forgotten Realms, so some things will...