Well, let's think about this. First off, I remember someone pointed out earlier in this thread concerning the Best Buy demo, if my theory of 5x10 is correct, they organized the rows the simplest way.
Mario/DK/Link/Samus/Kirby/Fox/Marth/Sonic/Pikachu/Pit
Now if this is correct, this means that Sonic's column would naturally have 5 slots. If that were true, even if Snake came back and Pac-Man made it in, that would leave 1 slot remaining. Tails, being a 3rd party, could naturally fit into this under Sonic. Now let's take a look at our close up Twin Tailed Fox and our close up Fastest thing alive
First off, I must say the detail they put into Tail's is quite good. The outlines are all where they need to be. The hand where it is "inside his foot" area has no outline, only the area around it. However, the hands of tails are much more shaded around the wrists. For the rest of the outline, as far as I can visually tell, it's the same as Sonic, the outline only covers the edges of his body, and nothing inside, such as the hand example I mentioned. What about the shoes?
The shading around the soles of Tails seems a bit different, however that could be attributed to outline thickness.
My final conclusion? Hex do your magic, this as good as I can do x.x
EDIT: As pointed out, the mouth is off from what Tails usually features. However his smile does appear to be larger than Sonic, part of the detail could be hard to make out due to the angle.