The movement to fully legalize Aadhaar usage has now reached its crescendo, as Govt. notified all but one provision of the Aadhaar Bill (Targeted Delivery of Financial and Other Subsidies, Benefits and Services). In layman terms, this means that Aadhaar Card has now legal backing, and the Govt. of India can (and will) impose its usage forcefully, across every Govt. scheme.
The only exception to the mandatory usage of Aadhaar card is the issue of privacy, based on which Supreme Court has still stop its usage. But privacy is a subjective matter, and there are tons of legal loopholes to make this issue a minor one.