What does this mean about the size (and thus feasibility) of a circuit required to factor a cryptographically interesting number, say, to be generous, RSA1024?
Estimates of the cost of RSA1024 use explicit circuit constructions at the target size, rather than extrapolating from the 4 bit case. So they implicitly account for the discontinuity being pointed out in the post. So this post has no impact on those costs.