Well, the SP is a much newer body design than the Leica M9. The Leica M9 dates back to 1954, and gets its looks from the M3. The SP was born much later, 1957. Same year I was born. Much more modern. It's the split top deck (Battle Cruiser deck) on the SP and the long RF window.
But I am not holding my breath for a D-SP. The Amedeo adapter on the M9 will be as close as I get. WAAAHHHHHHH.