It’s not an impossible ask. The resulting front element size of about 140mm is the same as the Nikon 300/2, or Canon 400/2.8, 600/4., 800/5.6. These lenses are pricey but not unaffordable.
The ability isn’t that crazy either. Wide-open lenses have football-shaped highlights in the corners and a related substantial light fall-off. Stop down to f/1.4, though, and you could have a circular highlight from center to corner. Then, add a DS filter and light transmission and total amount of bokeh is again cut in half, to the equivalent of f/2.0.
But while the bokeh amount is the equivalent of f/2.0, it is spread in diffuse balls of light no matter where in the frame an out-of-focus highlight is. The result would be the most beautiful portrait lens of all time. Its photos would be recognized by all, its edgeless, circular highlights even in the corners unproducible with any other lens.
This is what I’d call a “halo lens,” much like the EF 1200mm/5.6, or the tilt-shift lenses, that people who don’t own Canon can recognize the work of instantly and yearn to have even the theoretical possibility of shooting. Other examples would be a 50/0.7, similar to the half-dozen or so examples used by Stanley Kubrick to shoot Barry Lyndon.