Thanks for the summary!
I do hope to have time eventually to watch the actual video.
Did he ever say which additional 8 skills he'd keep for L2, assuming the other 8 are all the classic ones from L1? Surely not something like superlem?!? I see he likes the ones with the "cool" factor, the ones that are more complex and hands-on. But I suspect if he actually had to play through many levels that make you use those skills over and over, he's more likely to come around appreciate and stick with the simpler but useful ones, like jumper, for the extra 8 skills.
I wonder, if L3 had not been tile-based but pixel-based, would Mike actually have liked it? Feel free to correct me with counterexamples, but the tile-base aspect of the physics doesn't seem integral to the game, I believe the game could've been implemented pixel-based and still retain all the same features it has, and seems like it'd play almost the same as being tile-based.
Given that L1 and L2 are shipped in floppies, I'm quite sure they'd make sure to exclude the editor in shipped binaries if only to reduce the disk footprint. Even with the primitive programming toolset at the time, I believe it's still quite feasible to conditionally exclude editor code from compiling into the release build.
I think our best evidence for the editor not hidden in the shipped product, at least for DOS L1, is that we've pretty much figured out all the files where the graphics are stored, and we've scanned the EXEs for ASCII text. You'd expect that if the editor still exists in some form that can be made functional in the game, you should be able to find some graphics and text that are uniquely the editor's. On the off chance that maybe there really is some remnant of editor code still accessible either via some hidden key sequence or via trivial hacking, I still suspect it would still fail to run properly without the editor-unique graphics and text.
I also want to argue that the person who made CustLemm probably could've unlocked (and add whatever assets are missing to make it work) any possible hidden built-in editor in the game, if it was truly present. That he instead wrote his own LemEdit editor would seem to suggest there isn't any to be unlocked from the game.
Granted, this is all just DOS L1. Maybe the situation is different with Amiga L1 or one of the L2 ports, we've worked far less on those ports to ascertain.
Even during the brief time Mike hung around on our old incarnations of the forum, he was basically not active at all with custom levels, I don't recall him ever playing any. So it's no surprise to me that he's probably unaware of Lix, NL etc. Plus he might have permanently lost track of this community during one of our past site moves, and was no longer around at all by the time Lix and NL became widely played here.