Do BA really need a formal arrangement with an airline like Indigo?

I mean all the desi carriers have bent over backwards in the past to help the foreign airlines with domestic feed, and nothing's really changed. So what's really to gain now?

A code-share will put little more than a new sheen on what already exists anyway, right?

Or am I missing something?

True. But more than likely they will be able to have one up and running - in addition to meeting all the other alliance entry requirements - and actually join an alliance in less time than it takes the National Beggar to empty the begging bowl.