I was just wondering when ASEAN becomes a a full single market how or will it affect re entry permits within that region? Outside ASEAN things will be as now but what about inside, will it be like the EU that you can travel freely across the countries that are in the block? Just wondering it might encourage more ravel in th area if we did not have pay 1000bts a trip and another bit of the passport taken up.

I think it is pointless to consider what might happen in 500 years time, and those are about the timescales we can expect for a true ASEAN free trade area.

Nothing will change for those not a citizen of a ASEAN country. 

It will never be like the EU with open borders. There will still be limits on the allowed stay.

We might get a tourist visa type permit that can be used across the area. Not sure if that would benefit Thailand much, but might help the less popular neighbouring countries.

One needs to differentiate between the free movement of goods ("single market") on the one hand and the free movement of persons on the other hand. They are the subjects of two different international agreements and may not necessarily cover the same list of countries.