Great trip reports. Just one thing about the Singaporean passport visa exemption into Myanmar, according to my immigration contact, that's only valid for entries into Myanmar by air. By land, you will still require a visa, but luckily, 3 out of the 4 land border crossing points from Thailand accept the e-visa, which you can apply for online and it is almost always approved the same day you apply (provided it's a weekday) with the confirmation letter sent to your email.
Since the e-visa system entered into force, no Asean nationality that previously got 14 days visa free at the Thai land borders can avail themselves of visa-free entry anymore. It only applies to entry and exit by air.
Unfortunately still no changes to the law requiring advance permission and a guide to enter Myanmar by car or motorcycle but the process is becoming more straightforward and streamlined, though this largely depends on which travel agent you apply through.
The so-called trilateral highway is nothing more than "clickbait" at this stage. A highway linking the Thai border at Myawady (or Myawaddy) to the Indian border at Tamu already exists and is in fairly good condition for the most part, with the 45km Myawady to Kawkareik bypass road greatly reducing travel time to the plains compared to the old road. The next 90km stretch to Hpa-an is narrow and not in the best shape, but is slated for upgrading soon.
After Hpa-an, it's good all the way to Mandalay. Not sure how the road from Mandalay to Tamu is as I've never been there, but I have heard it's in fair condition and currently being upgraded.
I read in an Indian publication sometime last year about a plan to build this "trilateral highway" with all traffic traveling on the left hand side of the road, as in Thailand and India, which the Myanmar government has agreed upon. Should this be the case, then obviously a brand new, dedicated road would need to be built. So far there is no evidence there is such a plan, only the existing road is being upgraded but as it's a road shared by both local and long distance traffic, there is no way traffic on this road would drive on a different lane to the rest of the country, including adjacent roads branching off from the existing road. Such a bizarre arrangement couldn't possibly work - only a dedicated, fenced off road would.
I wouldn't put my bet on this much hyped up "trilateral highway" becoming a reality anytime soon. It's probably nothing more than a marketing gimmick.
If it does happen first of all, Thailand would need to allow Indian vehicles in without a permit, while India would need to drop their carnet requirement. Even more importantly, Myanmar would need to allow unrestricted transit of traffic through it's territory and thus drop their advance notice, tour and guide requirements. Also, India needs to upgrade its highways all the way to Kolkata, given the state of infrastructure in their north-eastern states, I can't imagine this highway would attract much interest from logistics firms or even tourists, given the vast distances, long travel times and bad roads along the way.
For us adventurous motorcyclists though, it may well be quite a dream.