First of all, hi everyone. I joined a couple days ago during the "leak frenzy", but I wanted to give my two cents about the matter.
Personally, I think this is NOT the final roster. Here is my reasoning:
a) the CSS, as it is, doesn't really make sense if that's the final roster. Whether or not the Mii Fighters will be included there (I think they have their own "Custom Characters" page as shown in one of the menus, by the way), you'd either end up with 49 slots (as they are in the CSS picture) or 50 slots (with the Mii Fighters added). Now, considering Sakurai's well-known OCD, the second-to-last row seems... off. Why didn't just put Shulk along with Ness, Falcon and the others to create another neat row of 9 characters and leave the 3 third party characters by themselves in the last row? Here, the second-to-last line is off center, which doesn't look very Sakurai-ish. Of course, one could argue that in case customization is on the Mii Fighters would take the ninth spot in the second-to-last row, but still the position of Shulk in the roster (not to mention the "clone corner") are really weird, especially considering the past rosters.
b) SSB4 is quite unique, in that is comprised on two different versions that aren't being released simultaneously. Since it's pretty clear Nintendo is counting on the WiiU version to re-launch their home console, it wouldn't be that smart of a move to have that version being completely "spoiled" by the 3DS one in terms of the entire roster of characters included (since, let's admit it, one among the many best things about SSB is to speculate about who will or will not be included). That's why I think that what we see in the CSS leak image will be the final roster for the 3DS version... for the time being. When the WiiU version will be released, that version will include the remaining four/five new characters, that will be at that point unlocked on the 3DS version via a free DLC or an update. That would also explain why the supposedly existing "extra character" do not appear even if that version is the one show to the ESRB (and thus, theoretically, the final one): the one leaked is the 3DS version, but if the other characters are included in the WiiU version, they will be shown when that version of the game is evaluated.
Having said that, I have no idea about which characters would actually be included, in case my scenario turns out to be right. I personally believe in the Ridley/Mewtwo/Chorus Kids/Dixie leak, but that's just wishful thinking.