I really miss having that extra screen space you get with an extra monitor. But just like you I can't justify carrying a monitor when traveling. I make due with the 12in on my Surface pro. I do carry a cable and hookup to anything available like a hotel room TV with HDMI for example.
We can dream of that 40in foldable monitor but my hopes are not high.
RE: Why I Wish I Can Travel With an External Monitor