Cross bikes are an excellent transition from mountain to road. I went from road to mountain. I've taken my road bike on dirt and gravel, wishing that I had a cross bike. You'll definitely be able to hammer out more miles on a cross bike, than a mountain bike and it'll be more versatile that a road bike (I like to throw a loop around Illiniwek in on my road ride sometimes).

Mind if I ask what your reservations are about going straight to a road bike?