First of all, Aadhaar is not just being used for welfare schemes. It is a giant database getting linked to everything. I wouldn't be surprised if it will soon be mandatory for booking flights. Plus much of the database has leaked. You can find thousands of Aadhar cards online just by googling.
As far as preventing 'leakage'--the best approach would be to not subsidize products but to move to direct benefits transfer (like food stamps in the US.) The government has been doing this anyway, for things like the LGP cooking gas subsidy. But even that has been problematic in terms of implementation. When it comes to solving corruption, we can't let technocratic bureaucrats come up with solutions in air-conditioned offices and hand-wave away the deprivation and other problems their solutions cause on the ground.
As far as preventing 'leakage'--the best approach would be to not subsidize products but to move to direct benefits transfer (like food stamps in the US.) The government has been doing this anyway, for things like the LGP cooking gas subsidy. But even that has been problematic in terms of implementation. When it comes to solving corruption, we can't let technocratic bureaucrats come up with solutions in air-conditioned offices and hand-wave away the deprivation and other problems their solutions cause on the ground.