Banning inputs from registering is pretty much the same thing economically as a fidelity bond. In both cases BTC is tied up and unable to be used for the intended purpose.
A true time locked fidelity bond could potentially be a stronger defense as the funds couldn't be used for anything else during the timelock. But that's pretty disruptive to users of Wasabi. So there's trade-offs to implementing stronger protections.
Re: confiscation, I don't think there is any way to do that with pure on-chain scripts even in theory, ignoring current scripting limitations. The problem is how do you prove to a third party – script validators – that an entity failed to make a network call in time? With trust you could do that, eg with a multisig. But I doubt that Wasabi wants to have that kind of control over peoples' coins.
