Other than Myanmar, only Indonesia and Thailand that has the necessary means and geography to actually sustain combat near the bay of Bengal. Others are either too far away or they don't have the means to sustain assets near Bay of Bengal.
Yeah, the thing is if Myanmar and Bangladesh get into conflict there is no practical reason for Indonesia to come at Myanmar defence.
First, Myanmar is a pariah regime.
conflict will likely to occur because of their fault.
And in that case, you can definitely expect US and EU to come at Bangladesh support politically on the international stage. Not only because 80% percent of export goes in to west but also more importantly, because of 'Myanmar/China/Russia equation'
And even if still there is an actual threat from third party to get involve in the conflict we will just give the USA Saint Martin Island ( that they were craving for many years ) and you can expect a carrier strike group to move into the bay of bengal )
Secondly, ASEAN is not a military pact anyway.
Thirdly, As far as I know Myanmar doesn't hold any meaningful political or economic value to Indoensia either.
In addition to that, after all, Indonesia and Malyasia are muslim countries. ( keep your REALPOLOTIK out of here for a second ) And religious solidarity does effect foreign policy at some extent, specially in muslim countries.
And for the same reason you can expect all Arab and Muslim countries to come to Bangladesh's support politically if Bangladesh's sovereignty under attack.
Note, If you want to reply could you take the discussion to 'history and war' thread?