So I have the answer about working on Monaca / Onsen while you fly - seeing as that is what I am currently doing (btw, I swear they are making the seats narrower every month!). My first test was to just connect to in-flight wifi but not actually buy the wifi to see if it would communicate through the router as each device would obtain a valid IP address. While this should work in theory, I could not get past the first hurdle of LocalKit requiring you to login to Monaca.io. The same goes for the debugger.
So, the short answer is, offline development / debugging is not possible using the Monaca tools. A major bummer as I was really hoping to just be able to use Atom with the inspector and the preview tool.
On the plus side though, this forced me to buy the $39.99 in-flight internet so now I can write on the forums and share this experiment with you all! :stuck_out_tongue_closed_eyes: