I think we'll get the low end of 45-50. I think saying over 50 is wishful thinking, but the direct made me reevaluate how many characters are in this game. I had originally thought 45 was a nice, likely number, but perhaps slightly too high. Post direct I'm increasing my count.
There are multiple reasons for this; first of all I had always considered movesets more than slots, and had assumed that Pokemon Trainer and ZSS were going to be cut. I had theorized that transformational characters might be too difficult on the 3DS, as I do not know what its memory is capable of, whether or not it could afford to keep more character models on the backburner. This dropped the number of Brawl's unique movesets to 35, meaning we would get 10 more new movesets. Well, I had predicted one of them would be Mewtwo. I had also predicted that Sheik would be cut in favour of Impa and Ike would be cut in favour of Chrom, both of which would inherit an updated version of their predecessor's movesets. This would have meant 12 'newcomers' with 10 new movesets, and I thought that was pretty reasonable. Ultimately I did not think they would have the capacity to add more than 10 movesets to Brawl's lineup.
However, having seen some of the newcomers and some of the changes to the veterans, I have been forced to reconsider my thinking. The move away from transforming characters as made the separate pieces FAR easier to balance in relation to each other. Along with this, many veterans and newcomers have had their strengths and weaknesses magnified, making the balance between characters easier to manage. Because I had only limited myself to 10 new movesets based on balancing difficulties, and said 10 was a minimum because any less would be too disappointing. With the perceived focus on making sure characters are more easily tuned and balanced, I now suspect more than ten is possible. Add to that the return of ZSS and I am definitely over 45 now, albeit not by much.