Ah, you've misunderstood me. I've never said that there are apps that allow full screen on a Chromebook. I've said that your claim of them not being full screen "because app developers build apps for particular screen sizes" hasn't been true for a while. That isn't the reason they don't have full screen versions (well, at least with Evernote. I've noticed the Vine one seems to be the mobile version only released as a panelled app by design). It actually seems to be limited by the version of Android on Chrome OS.
As for apps that appropriately scale to screen sizes, most of the Google ones (Keep and YouTube being good examples of redistribution of assets) have done that for a while, and a few others that I cannot for the life of me bring to the front of my mind right now. Evernote is another example of building once and having the assets move according to screen real estate. That app should be perfectly capable of adjusting without warping, easily stretching itself out to full screen without problems. And yet it doesn't, leading me to believe that the version of Android is limiting apps at the moment (presumably to make it easier for those app developers you mentioned who haven't translated their apps over the past couple of years).