This is by no means official but it comes from people I know that are living over there as well as people who have recently traveled to areas in SE Asia. At the moment it can be a bit troublesome getting around from country to country because one country has totally different entry requirements than the next and almost none of them are granting visas on arrival. This is further complicated by the fact that some countries have a "border hop" situation in place in order to renew visas which is a rather strange process used around the world where you stamp out of whatever country you are in, stamp into their next door neighbor, then without even staying in the 2nd country at all you come straight back with a new visa.
It's a stupid process but it is used around the world. It makes no sense to make people jump through these hoops and I have no idea what their justification could possibly be for perpetuating it.
The point in this particular situation is that this "border jump" is not an option in most places these days because even if you are not planning on staying, you will still be subjected to the same controls as people who intend to MOVE there. Some countries the borders are almost completely closed to travelers as well.
Thankfully, there are rumblings and rumors about all of these restrictions and annoyances being eliminated or at at least unified under all of the countries in ASEAN by 1-April-2020. What this will mean is that there will be a certain condition that has to be met to enter ANY of the countries, and if these conditions are met, you will be allowed to travel between ALL of the countries involved. This also includes the citizens of these countries.
Now before anyone gets too excited you can go ahead and bet your bottom dollar that one of the conditions will likely be double-vaccination as well as PCR tests. There are no talks about the details of said test and how much they will cost or if the rapid tests will be used but if there is even any talk among these nations about making getting around a bit easier, I am for it!
Most of the ASEAN countries have taken a massive hit as far as their economies are concerned because the tourism industry, which many of them rely on quite heavily, was all but completely eliminated over the past 2 years. There has been massive unemployment, huge losses of businesses, and according to people I know that live in some of these countries, just a general sense of depression among the thousands upon thousands of people that depended on this industry for their lives.
Even though it is only a rumor at this point, hopefully there is some truth to it because this part of the world is one of my favorite to travel around in and it also has the added bonus of being one of the least expensive vacation destinations in the world.
Let's hope that it happens!