From a spotters point of view, it might be nice to see a 747 in SN colors, but it is just highly unlikely. I think the chances are bigger to see a 747-8 in SN colors in 10-15 years time. But still unlikely...
That additional cargo capacity is nice when you can fill it. CargoB's original intention was to become a player only on the African continent. Soon they started to fly to South America, because their was more money to be made, and even that was not enough...
I think SN is doing a very nice job by adding LH capacity with a steady pace, without loosing much profit.
The A330-300 is (one of) the best aircraft around for SN for now, they dont really need the range of the -200. I think the best option for SN is to order new A330-300 asap, HGW variants with a max T/O of 238tonnes.
The first 787 won't be much more fuel efficient than the latest A330, which proves how efficient the latest A330 are. The 787 will obviously improve and become a real game-changer, but it is sold out until 2018-19-20(?).