I'm in agreement with Tucy I think most of the musings about NorthPark expansion have always been contained in this forum. I think the DallasNews covered a hotel rumor once but besides that its mostly our sugar plum dreams planting the seed that something is in the works.
I think NP developing its North side lots with mixed uses and more parking garages would be great. Office, hotel, condo and restaurant/retail space would all do amazing there.