The biggest hurdle might be if the public would be tolerant of such extreme angles. It would feel like a slow roller coaster.

Yeah I was thinking it would suck for a passenger which is why it would only be useful for temporary bypass situations, since tunnels can clog up if cars fail. But that's a lot of engineering just for that one usecase. But I do except tunnels to become much more popular as cities become more dense and cars become automated.