If there is to be another Empire, I would like to see it be composed of a dozen or so species. Not one ruling species and eleven second class associates (dominion), but have them all be up front.
With some federation/Starfleet people, have some of them be old enemies, perhaps from centuries past. Old bad blood.
Like to see some Starfleet people who were outside the normal range in terms of size. Children with makeup and a voice over to appear as adults would be one way to do this. Have the turbolift doors open and a seven foot tall officer briefly ducks to exit onto the bridge.