It's not madness, it's impossible. Do you know how heavy sheilds are? There is no way you could possibly work both without exhasting yourself in less than a minute. You would not be able to move fast enough to block any attacks. The reason a sheild works is by showing that side to the enemy to cover yourself. With two sheilds what do you do? Stand face to face with someone leaving most of your body unprotected?
There are just so many reasons that double sheilds make no sense, and is literally impossible.
If what you are saying is correct, then the entire shield mechanic in Skyrim is borked because it relies on timed blocking.
Besides, a character gets better at dual-wielding shields the more he does it... Might tire him out at first, but soon, (s)he'll be swinging around Roman Scutums (Known for their devastating shield-bashes, Dungeons+Dragons nonsense be damned) faster, more frequently, and for longer than anyone else can handle even two daggers!