Your question begs many questions. Will anybody in Nepal, Bhutan or Bangladesh will be willing for it. They will be killed by 'the state' there.
However, all the things you have listed can be possible through an economic union of these countries. Now the governments are acting as stumbling blocks and working at cross purposes willingly. Even in an economic union, India being far more larger will definitely get lion's share as a natural process. Will the others like that?
SAARC was started with the same end in view. But the intense cut-throat rivalry and cussedness has made this organisation virtually defunct that degenerated this into a platform for mud slinging, wild and unacceptable accusations and all that. Much worse, trade which should have normally prospered has acquired a motto 'how not to trade', because then the countries will acquire a 'stake' that will be detrimental to the 'military'. Being a very big country, India is able to take these pinpricks in her stride. But this may be a pinprick for mouse, if it is to smaller countries. Adjacent countries who could import their requirements from the next country where it is abundant (that the whole world imports from it), get it imported from half way around the world. Nobody in the globe can beat this cussedness. Even in stories and literature of western countries these two are shown as the example of extreme rivalry.
There is an initiative for 'Bay of Bengal' community following India's 'look east' policy. This might hopefully isolate a country and the rest being in some way or other connected with 'Bay of Bengal' (Nepal and Bhutan want access to Bay of Bengal through India) may be an alternative to SAARC with new members added (Thailand, Myanmar & indonesia) will take shape. Bay of Bengal has always been a zone of peace, trade, culture and prosperity.
Two Germanys have joined, divided Vietnam became united and even Koreas may join but South Asia will not be the one that was in 1946. British should be given credit for that. They have some more credits up their sleeve - creation of Israel in the midst of Palestine homeland, creation of an abomination called Northern Ireland. Other countries like Cyprus has followed their mentor's (Cyprus was a British colony!) policy. Many men asked me about reunification in some form (you call it federation). There is a lunatic fringe working for 'Akhand Bharath' (unpartitioned India) who too strive for this goal, but with the proviso that India will dominate, much like the Serbs in Yugoslavia. This cannot and should not happen and any association will be of political equals, where all individuals have equal access to opportunities.I gave you some points to ponder over; think about it.
With this type of mindset in International relations, your dream will remain a dream.