There is a lot of work to be done for Ndigbo outside to be successfully encouraged to return en-mass. Igbos have an investment mindset.
You need to encourage them to return by placing the necessary infrastructure and the rule of law on ground.
Even then, not all Igbos would want to return, for Igbos are like Jews. Not all Jews have returned to Israel. Igbos prefer to have a global network. So, Igbo state governors should create a common service international NGO that can assist Igbos everywhere, and repatriate them from serious trouble spots.
But if a critical mass of Igbos outside can be encouraged to create a formidable presence in Igbo Land, it will go a long way in developing Ala Igbo.