About "Paa" - its commercial and critical success is largely due to the Amitabh factor plus Balki's persistent savvy marketing in the north/ hindi belt (this is not to trash the quality, but the kind of hype that went with the marketing of 'mudi mudi' in every other TV channel - had it been done for 'chal chalein', that album wud have become equally popular)
lets face it - Bachan himself has been down in the dumps getting infamy through all kinds of offscreen dealings - barring his 'kaun banega crorepati' success, his films have all sunk without a trace last few years - PAA is the brainchild of Balki and it has worked through a well-planned aggressive marketing campaign(which has its spillover effect on the success of music as well)
yet another thing to consider - there are 'n' no of camps in Bollywood - Bachan camp is just one - there are others, Shah Rukh camp, Aamir khan camp, karan johar camp, rajshri camp, hrithik-rajesh roshan camp and a few other camps - these camps often might intercollaborate, but seldom they look outside and they have certain preset teams of technicians including composers - IMHO, the possibility of any of them working with IR (despite Paa's success) is very low - even if they did approach IR, our man in one moment of eccentric indecisiveness, might turn down an offer!
and then we have this tiny bunch of creative guys like sudhir mishra, vishal bharadwaj, pankaj kapur, and a few other creative guys with theatre background making offbeat films which may or may not be commercially viable - these guys MIGHT want to work with IR, but even if they do, the chances of success of the output commercially wud be 50:50
this is all based on my understanding of whatever little i have been seeing in the media online - what IR needs in the hindi film circle, post-PAA, is a real kickass album like what shankar-ehsan-loy did with 'dil chahta hai' - an album that will be played on FM and by DJs - an album filled with 'mudi mudi' type nos! and it has to be in a film thats hyped up and silly enough to be a hit!
our man OTOH is "un kani vizhum yena dhavam kidanthaen" type - expecting fate to take its own course - in deep contrast to another composer who is ambitious enough to make proper use of his collaborations to further his dreams!
its upto IR entirely