I wouldn't assume at this point that the unknown Cylon is the number 7 or somehow special. the final Cylon could be almost anyonebut then since this is television it will probably be the most shocking revelation, So probably someone we expect the least.
I'm kinda hoping they [6's et al] manage to revive the 3's.
I'd say they must have just had to roll with sharon = 8 since that was established early. it just seems odd, especially since they are [for whatever reason] not meant to think about the other 5.
I wonder how thngs would have played out differently if Cally hadn't killed "Boomer".
the number 6 model has also gone by several other names so far.