Don't be silly to only think for yourself.
A language for the region should be the neutral language without the baggage of the people in other countries.
Whether you are from the most populated country or minority one, all should use the UNESCO recommended neutral language to save more languages from dying from the planet earth.
If you do not know what Esperanto is, read Malaysia Esperanto Studies Group page. Go to the social media like Face Book, Twitter etc and search Esperanto to see how the people are using Esperanto.
Selfish will let you to kill yourself in future. No other national languages to be used for the ASEAN communal language. Only Esperanto is.