Alexensual suggested a great way to have a Classic launch without Sharding
Let's say the server is Archimonde, there will be 10 Archimonde servers named Archimonde 1 through to 10
All of these servers will be merged into one Archimonde server after the initial launch when the playerbase has stabilised and the number of players is consistent after let's say 1-2 weeks
So initially there will only be one tenth of the population of the total realm at launch not to have too much traffic in leveling zones and still keeping the community alive and seeing the same players around without them phasing out
It doesn't necessarily have to be 10 versions of a server it could be any number really just to keep the numbers stable on a server for the levelling experience
This has been the best solution I have heard so far while not having to use Sharding on launch which no doubt blizzard will have to manage the launch in some way or another to reduce player numbers in zones