Neither option looks like it will work. Need to sync layouts / graphics / images, need embedded fonts for printers (not just an image of the indd file), as well as live updating links for text and tables...
What about using "Master Pages" to live link between the digital (tabloid pages) and the print ready (dual portrait spread) pages? I am already going to be using Master Pages as the basis for most of the print export, so I could base the new "print" Master Pages on the "digital" Master Pages that I use for design / updating. I am going to have a ton of Master Pages and a massive working file, but seems like it might work.