I'll be pretty disappointed if they don't release the Stage 3 alongside this.
Until then, we should compare the teaser video with the electro 5D.
1. Screen: This looks like the same screen to me.
2. Knob below screen: The knob in the video is closer to the screen than the one in the pictures on the website in the "click to enlarge" section on the right. There is a split/transpose button between the screen and the mix knob in these pictures. However, I noticed that in the picture of the 5D in the banner at the top of the page, the knob is closer to the screen and there is no grey button above it. Instead there is a black button below. This means the video could be a electro 5 in a different stage of development. (like the banner pic)
3. Segmented LED displays: On the 5D there's a piano section to the left of the program section, and a synth section to the right. Both have red segmented LED displays. These two displays seem roughly to be in the same place on the 5D and the keyboard in the video. However, on the 5D- the instrument selection indicator (the six small LED triangles) are above the segmented display- while in the video- it appears that the selection indicator is above the display. This makes the video keyboard look different from the 5D pictures, but it's a subtle difference.
4. Green LEDs: There appear to be several green LEDs in the video. The only ones I can see in the 5D picture are the split indicators above the keys. Perhaps this is a good sign?
5. General Layout: The layout of these two keyboards seems VERY similar. Disappointingly so. The LED spacing of the "part lower" and "part upper" sections seem to be the same, and the four "ABCD" program selection button lights seem to be in the video as well. It does look, however, that in the video- these lights are shifted to the right, and there are some extra green lights to the left of them.
Conclusion: These look like different keyboards, but only slightly different. It seems more likely that the video is of an Electro 5 in a different stage of development rather than a completely different keyboard. I say this, while still clinging to the hope of a Stage 3 announcement.