I am sure that bitcoins can influence the local currencies of developing nations. But if this is actually weaking or more a strengthening remains to be seen. Of course the IMF is against crypto currencies because he can't go to national governments and ask for crypto money to lend out to troubled countries. For developing countries with weak local currencies I think they will get positive effects from crypto investments. For example if a country struggles with inflation their currency will fall, but their investment in crypto currencies will not be affected. Its a good way to reduce the dependency on the local economy.