So I am on the plane right now flying to Istanbul. Nobody cared about my old passport. When I showed them travel document it just confused them, they (United & turkey airlines)only cared about my passport.
I am not saying you don't need travel document but looks like airlines aren't really implementing this mrp passport rule yet, I am sure they would be strict if I was traveling to USA instead of Nepal. Let's see if they care in Istanbul while boarding plane to Kathmandu.