Construction to begin next month according to Work Live Laos
http://www.worklivelaos.com/laos-and-myanmar-to-begin-building-friendship-bridge/#comment-907

Interesting enough. The bride is being build next month and still unclear how much the project cost, design and estimated complete date. Why me worry!

Strange location as that is one of the east populated sections of the Mekong, on either bank of the river.

As Hacky said it isn't built yet. Then again they've been talking about it for years. It's 40 or so kilometers to a hard surface road to Kentung, and don't forget that the "locals only" border at Muang Sing is busy. There's one copper mine between Long and Sing and there was a lot of surveying being done in the mountain E of Long for another. Of course that means nothing about a bridge further on but it's hard to say what motivates the Chinese.
Might not cost too much, river is small and narrow up there.