I found my way through genesis: spirit, and got the nemesis, but even though I took that path, for the hell of it(and to see if another one of those item panels was back there) I went through the reservoir. Go into the waterway, then just use the door again. You'll be at Genesis water. Pretty sure that's a bug.
In addition, if you go back to grasstown and enter the construction room, and come back out, that script that has the floor crumble happens again(and while this is probably necessary to some point to get the chest in the shaft you fall through, the fact that entering sand zone puts you inside a solid block means that saving in genesis: air means you have to start the game over. Thankfully, I had a backup save). Also, what use is the explosive?
I never reached a "demo ends" cutscene or anything, not even a locked door, unless you count the one in the egg corridor, and I was just checking the area before scaling the chimney. Anyways, once I was in Oblivion: Erosion, there was all sorts of scripts from the original cave story still in place, as well as doors that go places in the game that clearly aren't intentional(yet)... Even one that goes to a room from the original cave story(where you find the scientist who was transformed into a mimiga), from which you can go to the original outer wall, and original egg corridor, and glitched Dragon Sisters room. Seeing that, I basically took the hint that I had reached the end of the content.
Though I have to wonder where the third reagent for the gunsmith is... I have the lens, and the autocharger, where is that last thing hiding? Or is that just another thing I have to wait for in the final version
Also, the area Genesis: Light, and the accompanying boss were epic.