Hold it right there.
The proposal, as I understand it, suggests that I would be able to travel from Thailand to Vietnam, for example, without a visa, but I have seen nothing to indicate that
1. Vietnam would not put a stamp, of any size, in my passport saying something like "Entry permitted without visa;
2. I would be allowed to travel back to Thailand without a visa for Thailand.
Never underestimate the ingenuity of officialdom of any county.