Some have speculated that it might be an egg, which would actually fit given that Easter is coming up. While there is Billy Hatcher, that would seem strange, given the almost underwater look it has, and the association with Nintendo. Of course, Bayonetta 2's going to be on a different platform than its original release, so the possibility
is open.
However, I did actually take the time to try and measure the spherical object some in pixels.
At its widest point it's about 314 pixels. This is moreso so I know where the diameter is, so I can compare the top and bottom halves, however. The cyan line was used to find a more or less equal space on the side of the sphere; I'd give a margin of error of one or two pixels; the red line was used to help me determine where the diameter was most accurate.
Now for an "egg test," in yellow lines. For it to be egg shaped it's logically going to have a different measurement from the central diameter to the edges going up and down, and more than a few pixels to adjust for human error. Now, logic says that if it's egg shaped it's going to have a steeper incline on the top than on the bottom. It doesn't really matter where I put my vertical measurement, but the difference between inclines will be greater the further I am from the edge of the diameter, so I put it very close to where the object's top half currently ends.
We have 86 pixels on the upper half and about 88 on the lower half. With margin of error taken into account... yeah, looks like it's just going to be a sphere. It is still somewhat possible this will change but... it's unlikely. In Tokyo it's the 26th, so we have only two more days.
Regardless, it shall be interesting to see what they have planned.