Etihad Guest announced a new partnership today: Effective immediately, Etihad Guest miles can also be redeemed for award flights with Bangkok Airways, and vice versa.
Bangkok Airways owns three airports in Thailand, meaning there is (almost) no competition on those routes. While cash tickets cost around €75 to €120 depending on the date, you can book an Etihad Guest award ticket starting from 6,043 miles + approx. €5 in taxes and fees. In economy class, of course:

In principle, transferring Amex Membership Rewards at a 3:2 ratio is possible. However, with an estimated value of 1 to 1.5 cents per Etihad mile, this is generally not particularly good value anyway. On the other hand, if you have Etihad miles lying around with no other use for them, this option makes much more sense.