Myanmar and Thailand are doable but there is one huge negative thing and that is that you will need permits and guides to ride through these countries. You need to arrange those permits well in advance especially the Thailand permit as there is a lot of additional paperwork needed to get the permit.

For Myanmar there is no way to avoid these rules and the country was just opend for overlanders 3-4 years ago. Its expensive but not too bad, I have heard overlanders crossings on 10 days trip including guides and oermits paid less than 1000 USD with accomodation and some meals included.
For Thailand which overlander earlier on could roam freely around in you know need to get permits and have mandatory guides. These new rules came last year 2016. There seem to be some minor bordercrossings especially between Cambodia and Thailand and Malaysia and Thailand that dont enforce these new laws and still hand out 30 days temporary import documents for foreign vehicles. But if youre coming from the Myanmar side my understanding is that there is no way to avoid permits and guides when entering Thailand.
And remember also - you cannot just rock up at the border and get permits there. You need to contact a travel agency in Myanmar and one in Thailand well in advance and send paperwork etc. For Thailand I think I read that the agencies wanted documents 30-40 days in advance.

Another option is to ship from India/Nepal to Malaysia and avoid the hazzles but thats gonna cost a good bit too.

You can check out these facebook groups for more information:

https://m.facebook.com/groups/1024579897597702

https://m.facebook.com/groups/487122118151687

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