Like what? Seriously, it would be in effect a combination of the
existing Wimbleware service with a truncated H&C service, switching at
Edgware Road, not a bad location for such a switch.

That's combining 2 lines which have to mesh with a ton of other services
all around the 'circle' (ie, merging with the Metropolitan Line, Circle
Line, District Line) at a bunch of flat junctions (is there any grade
separation anywhere?), which sounds easier said than done to me.

Firstly, you'd have to assume that the existing timetable would allow the
services to run straight through - firstly, are there exactly the same
number of services on each line per hour? I doubt it? The minute you add
in another service on one of the stretches, that's likely to have a knock
on effect to the other lines, and once you start messing around with
those, they'll knock on everywhere else, surely? And even if they're
exactly the same number of trains on each route, do they arrive and
depart from Edgware Road with a convenient 30 second between them? If
not, that would impact other services again.

Or do they mesh in perfectly?