I am waiting for the final decision of the Supreme Court on this, since we have time to do the filings till July 2017.
The basic dichotomy is in the two laws passed by Parliament.
AADHAAR act passed by parliament mentions it is only for targeted delivery of subsidies and services to Indian citizens, and does not say it is mandatory to obtain AADHAAR number.
However the Finance Act 2017, amends section 139AA of the Income tax act requesting those who are in possession of AADHAAR to mandatorily update the same on PAN.
SC has reserved the verdict on mandatory AADHAAR-PAN linkage in that it is taking time to review the constitutionality of the same.
As submitted by the petitioners , If the court deems that mandatory linking of AADHAAR to PAN violates Article 14 (Equality before law ) and Article 21(Right to life and Personal Liberty) of a citizen, then it is likely to be made optional.
There is also another writ petition before the SC, challenging the AADHAAR act itself, as to why it was passed as a money bill.
There are strong indications when we read the transcript of the proceedings
..that the linkage will be deemed optional .
There is also lot of discussion around the Right to Privacy as an extended dimension of Article 21 - specifically wether AADHAAR is in violation of the same. This though has been referred to a constitution bench of the SC , and will , in my opinion , judgement will not be delivered earlier than the AADHAR-PAN linkage issue is sorted as it is a very complex multi-dimensional issue .