This sounds like "I know what you did last Summer". Maybe its inspired by RaGa's mysterious disappearance.
Fin Min should find some other way to get the same data, they shouldn't be trying to save costs by making people declaring the details. It is a tough and costly job but it is worth the investment (Both politically and economically) for building a better economic future of the country. Some steps that come to my mind: 1) Increase the scope of use of digital currency in normal life rather than hard currency. 2) Link Passport to PAN to Aadhar 3) Digitisation of land records there might be more of such steps.