The most likely consequence of implementing the ‘Unified Payments Interface (UPI)’ is Option 1: Mobile wallets will not be necessary for online payments.

UPI is a real-time payment system that allows individuals and businesses to transfer funds between bank accounts instantly, using their mobile phones. UPI simplifies online transactions and eliminates the need for users to enter their bank account details or net banking passwords repeatedly.

With UPI, users can make payments directly from their bank accounts, which eliminates the need to use mobile wallets for online payments. This means that users no longer have to top up their mobile wallets or worry about keeping sufficient balance in their wallets for making transactions.

Moreover, UPI transactions are secure, convenient, and offer several advantages over mobile wallets. For instance, UPI transactions can be done 24/7, and there are no transaction limits, unlike mobile wallets that have a maximum transaction limit. Additionally, users can make payments using their mobile phones even without an internet connection through *99# service.

Thus, with the widespread adoption of UPI, the need for mobile wallets will decrease as users will prefer the convenience of making payments directly from their bank accounts through UPI. However, it is unlikely that mobile wallets will become completely obsolete, as they still offer advantages such as loyalty points, cashbacks, and discounts.

Option 2: Digital currency will totally replace the physical currency in about two decades is a hypothetical scenario and not a direct consequence of implementing UPI. While UPI is a step towards a cashless economy, it does not necessarily lead to a complete replacement of physical currency with digital currency.

Option 3: FDI inflows will drastically increase is also an unlikely consequence of implementing UPI. While UPI can make transactions easier for foreign investors, several other factors influence FDI inflows, such as economic policies, infrastructure, and political stability.

Option 4: Direct transfer of subsidies to poor people will become very effective is a possible but indirect consequence of implementing UPI. Direct benefit transfer (DBT) is a government initiative that uses technology to transfer subsidies and benefits directly to the beneficiaries` bank accounts, reducing leakages and ensuring that the funds reach the intended recipients. UPI can facilitate DBT by enabling direct transfers to bank accounts, thus making the process more efficient and transparent. However, the effectiveness of DBT depends on several factors such as proper implementation, accurate identification of beneficiaries, and awareness among the target population.