IRS already uses to screen out questionable returns for human review.
The IRS historically does not reveal its secret formulas, for a good reason: the more you divulge to your electronic adversary, the easier you make it for him/her/them to attack you.
If the magnitude of refund that triggered a hold was built into a publicly-accessible interface (app), wouldn't that knowledge in short order be used to defraud the system?
Or maybe they don't *want* to do it, for good business reasons.