Even though it's an LLL you're talking about, I still think there are a number of things you need to consider:
(1)
Has a third party acquired a registered trademark or common law rights for that term? If not, it should be safe to register XXX.in even though someone else has already registered XXX.co.in.
(2)
If a third party HAS acquired rights, in what area of business is that term being used?
For example, let's say they are using the term in association with computers. Will you also be using the term in association with computers? If yes, then it may cause a likelihood of confusion among consumers, and there's a risk that the third party might bring an action against you for infringing on their rights.
If you are going to use the term in a different area of business, you still need to consider how 'well-known' the trademark is (see case of
Macmillan.in). For example, NBA and KFC might be considered very well-known marks - so if you were to register NBA.in or KFC.in etc, there's always a risk that they might try to get the domain from you.
If there is no 'well-known' status at issue, then it should be safe for you to register and use XXX.in in a different area of business than XXX.co.in.
I hope the above makes sense. If not, please let me know!
I'm not a lawyer. So if you need specific advice about a domain, I'd recommend you consult with an actual lawyer.