Don't believe all the hype. Yes there is some horrible shit going on in the border regions but Yangon, Mandalay and Bagan are safe and you won't be visiting anywhere else. If you want to visit Burma, do it now - it's only going to be a construction yard for the next 20 years and lots of tourists which can still just about be avoided now (went back twice in 2016). And Cambodia is only terrible from a democracy point of view. Unless you are going there to protest, again you're completely fine. You just need to know what to expect with the touts around Ankor Wat and know your maximum price for various things (Siem Reap is just full of tourists too - you won't stand out).
On the same basis as the above with political messes, you'd be choosing to avoid Thailand too - probably more terrorism threat there right now than Burma. But the reality is quite different and all are fine, just respect the locals like you would anywhere! And don't do what I did which was to organise a vigil in the centre of Bangkok by the British Embassy when Jo Cox was murdered - we ended up with 30 armed police coming to visit us...!