The IITs have built reputation over a long period of time. In addition to the facilities available, they can employ the best brains in the faculty and get the best brains as students due to this reputaion. Other RECs cannot become like the IITs just by adding some facilities. It will take a long time.
Suddenly converting some RECs will dilute the image of the RECs, at a point of time when the IITs are getting a global recognition, which helps the country earn foreign exchanges directly and indirectly.
Probably the nation stands to loose if this reputation is diluted. However as a long term goal this may be feasible under strict quality control w.r.t. the facilities, faculty, course content, publications, etc.
