I mostly agree with you about segregated infrastructure. But something going over 50KM/h belongs on the highway with cars and not in the bicycle lane.
Sure, it's dangerous, but how much worse is a velomobile with a flag than a motorcycle or scooter? Lots of people drive those. (And lots of people die on them too...)
First, my head is typically above the level of cars on my motorcycle and can easily see, with peripheral vision, around 300 degrees, meaning I can have a broader view of what's happening. Situational awareness is critical to staying alive around cages...err...cars.
Second, my cross-section for a car next to me is much thicker than a flag. It is at least the depth of my body and the depth of my fairing.
Finally, a flick of the wrist puts me far in front of the idiot trying to kill me. Acceleration is a crucial tool to staying alive on the streets around cars.
All of those are impacted by a velomobile. It's unfortunate, too, because I'd love to ride on.
On the other hand, on a motorcycle your head hits that car/wall first. On a velomobile, your feet do.
Also, the protection may be flimsy relative to that of a car, but it probably is a lot better than that of a motorcycle, for instance if you flip over and slide over the Tarmac for a few meters.
Your concerns are valid, though. The best way to cater for them probably is through a culture change. Having separate bike paths _and_ car drivers who are always on the lookout for cyclists because they always are there (example: www.youtube.com/watch?v=UlQYP4WN-5w) will help a lot.
Totally with you here. I'll play amongst the cars on my motorcycle, because I have superior acceleration, maneuverability, and awareness. I can see a problem coming and get out of the way before the driver even realizes they are putting me at risk. On a bicycle, I'd lose the advantage of acceleration; inside a velomobile, I'd further sacrifice the advantages of awareness and maneuverability. That sounds... scary.
I think the problem is going to be visibility. You're going to be really low to the ground and somebody looking over their shoulder/looking in the mirror might miss seeing you. At which point you are sideswiped and dead.
Sure, it's dangerous, but how much worse is a velomobile with a flag than a motorcycle or scooter? Lots of people drive those. (And lots of people die on them too...)