Taxation structure in india is very complicated. A unified GST is possible- and in fact required. The union government, state government and local government can share the proceeds of the taxes as per the recommendation of any constitutional body like Finance Commission. Even today although Income Tax or Central Excise duty or service tax levied and collected by the union but it is shared among union and state government as per the sharing formula developed by finance commission. There is no reason why such formula cannot be applied to GST.
It is not only required, probably it is indispensable if we want our manufacturing and service sector to be globably competitive. A complicated tax system, apart from increasing red tapism and corruption, reduces the competativeness of the country in a globalised world. It hampers growth of the economy.