I got 89% in class XII exams this year.Is taking a year off to study for IIT a viable option for me keeping in mind the the pros and cons of the new selection criterion for admission to the IITs and the NITs?

Hii

If you are damn sure abiut you will to have the tag of IIT by your side then its ok to drop but if there is slight hint of doubt in your endeavours then you must notdrop and be on wit the flow .
IIT is just a part of life its not the life so make sure you go on with new challenges of life.

Best of Luck