I agree with most of what you're saying here, particularly the historical roots of the design and the post does acknowledge the importance of the interface the BMW Motorrad brand.
But I think you make a false assumption about the potential order of operations - I'm not worried about signaling a lane change when I'm in the middle of an emergency, I'm worried about the emergency occurring when I'm in the middle of signaling a lane change. :-)
If you're not already covering the brake, there is no penalty due to putting the turn signal there. In my opinion, adding a linked-braking system to the pedal would do more to improve rider safety than moving the turn signal controls.
Too little and you might as well not do it, too much (and what is too much depends on a large amount of factors) and you're in a skid or you get launched over the front wheel.
The rear wheel brake is about 1/3 of the braking power, it is however quite safe to apply nearly all of that 1/3rd because the feedback is a negative one. The front wheel brake however has positive feedback, as you brake harder your front fork will compress putting more pressure on the tire increasing road contact and so on. Plenty of people that don't realize this and get on a double-disc brake bike and hit the front wheel brake too hard have found out that it is very easy to get flying lessons.
There are lots of patents on such brake linkages but I've never actually seen a bike that had one.
The front wheel does not need to lock to cause the bike to endo (back wheel raised). Simply preventing the wheel from locking up won't cure it IMO.
However, I can readily imagine using some gyroscopes to check that the bike is not flipping and if it's approaching a flip to release break pressure momentarily to keep the back end down. This would need to be very finely tuned as you'd rather endo into a stop with your tyre touching a truck than you would ride with two wheels down and hit the truck at speed. The amount of back-wheel air that you'd cope with will depend on the driver and conditions quite a bit.
Both front and rear ABS are very helpful in braking as hard as possible, and no more. From all I have heard, the modern systems are very good, if a little heavy. Ironically, it's the weight and size that keeps ABS off most bikes than can endo in the first place.
But I think you make a false assumption about the potential order of operations - I'm not worried about signaling a lane change when I'm in the middle of an emergency, I'm worried about the emergency occurring when I'm in the middle of signaling a lane change. :-)