I'm as sure as it's possible to be that SEN will never achieve 10 million. The absolute maximum in my opinion would be 5 million given its footprint and access and I doubt anything in excess of that figure could be achieved commercially under predictable circumstances.
I for one do not want to see it develop beyond around 3 million, certainly in the medium term. I very much accept that as a "good option" both as a supporter of the airport and as a traveller using it. As LTNman says sometimes less does indeed equal more.
I don't understand why this 10 million figure keeps getting mentioned by SEN management. Perhaps its simply to keep investors interested as I cannot see any logical reason for doing so.