Interesting pictures, indeed!
More and more this is looking like a mini 6 series as I predicted several months back.
And here is more proof (remember all speculation, just stroking my own ego by saying "proof")
The front of the car has very much the same dimensions. If you look closely it has that hoodline above the BMW emblem. The middle, where the grill would be is double the width of one headlight, just like the six series. Low kidneys, just like the 6 series. The six series has a mellow hood, and this 4 series does as well. The wheel arches stick out the same on the mule as they do on the 6 series. The front has the exact dimensions as the 6 series.
The rear of the car is where I think the 4 will distinguish itself from the 6. The lower pumper looks to be more shapely than the mule. I believe the tail lights will be similar but only as similar as the F10 is to the F30
Then there is how the mule drops its top. Just like the 6 series dropping his top. Notice it is the same system the 4 series uses. ALMOST exactly. Obviously the hardtop reverses the steps (folding the top first, then tucking it into the trunk, as opposed to the 6 opening the trunk first and folding the top in after.
The front of the headlamps also slide back into the wheel well a bit like the 6 series. Dimensions seem to be the same (although scaled down). But the body lines are very interesting on this mule. Of course it's too hard to tell what is and isn't there, but it seems like the main line to the 4 series will be a lot lower than whats on the 6. The six has a very distinguishable line that follows the door handles, this one doesn't seem to. Or if it does its not as sharp as the 6. There is also a second body line under the door handle on the 4.
I love speculating on these cars!
SPECULATION but very very similar.