Buriram Immigration is not moving to Ban Kruat.
The Ban Kruat story is that they are going to have a border checkpoint there that can be used for exit and entry to and from Thailand.
Two immigration offices will remain. One in City Hall and one near the stadium. It seems that the City Hall is the main one and fully staffed during office hours. I have never used the one at the stadium so am not sure about staffing levels there.
Luck of the draw maybe. When I was in Siem Reap airport we were on the 3rd aircraft to land in not more than 20 minutes. I was very glad I had an evisa.
I did say airport. I didn't need to extend as I was only on a short trip. Evisa made much more sense.
You have obviously never been through and airport in Cambodia.
Having an evisa ($36) online saves a load of time at the airport. Also saves a page in the passport.