I think limiting characters slots to less than the amount of professions there are is silly. Obviously we don't want to have people making 50 characters, but if it's limited to 4 slots, then we can only experience half of the game's mechanics from our own point of view. Then we'd have to delete those characters to have one of the professions we haven't played, which would make people angry/not want to play. I don't see why they would do this. I think that having 5-8 slots would be good: 5 still meets the amount of races (one of every race at least), and 8 meets the amount of professions.
I'd still prefer at least 8, but who knows; with the amount of content they have, who's to say we'll even need 8 slots?