Never had an issue with Eva. Flown 4 times from Heathrow to BKK in the last 9 months on an exemption stamp. Never been asked for onward travel, either.
I am currently on an exemption stamp and have extended. I was looking to come back for a bit longer and have a little more security with the visa situation. Still, it sounds like an Ed visa may not be secure. I’ll do a bit more digging.