This game's been enjoying something of a renaissance on the realtime speedrunning side of things. Thought I'd share the new discoveries.
Because Gens stores movie-start savestates outside the movie file for some inconvenient reason, all of these movies start from boot, so you can fast-forward through the first stage until they get to where they're going.
Medusa Bay map skip:
http://dehacked.2y.net/microstorage.php/info/1064819288/ecco-mapskip.gmv
None of us have the slightest clue why this works, or where else in the game it could be useful (if anywhere). I've personally tried bringing up the map in a bunch of weird places, but nothing. It's as simple as it looks: go to that spot & bring up the map, and the end-stage trigger just happens to be there when you cancel back out.
Lagoon skip:
http://dehacked.2y.net/microstorage.php/info/1172427106/ecco-lagoonskip.gmv
You have no idea how glad I am that this exists.
Spike shaft clip:
http://dehacked.2y.net/microstorage.php/info/1742255977/ecco-spikeshaftclip.gmv
Don't know of anywhere this is useful. Can be done through both left and right walls. Seems to have something to do with the flipping animation Ecco does midair if you keep tapping C.
Enemy bounce clip:
http://dehacked.2y.net/microstorage.php/info/1895339660/ecco-enemybounceclip.gmv
Same; don't have anywhere this is useful yet.
Weirder glyph skips:
http://dehacked.2y.net/microstorage.php/info/792616493/ecco-glyphtech.gmv
Given all the crazy stuff the TAS does with glyph skips, this was probably already known to some extent over here, but since none of us did I'm mentioning it anyways. If you idle, Ecco's idle floating will ignore the glyph's pushback (you can chain it by tapping forward to let it immediately restart from your current position), and then you can change the direction you're facing to get pushed out in a different direction. In realtime runs you can even sometimes save a badly-aligned skip by having it push you back into the correct alignment, but that shouldn't be an issue here. This particular gylph skip is the only one, to my knowledge, that was not considered possible before, at least in realtime, but is possible now (if glyphs weren't actual objects and didn't physically block so many passages, many more would be possible)... no idea whether this is slower or faster than the weird clip the existing TAS does at the end of Ridge Water, but it's worth a shot.
route improvements:
-going right across the ice at the start of ice zone is bad. The glyph is pretty much straight down-right from spawn.
-island zone: there's a better choice for getting the key glyph. Go right across the four islands at the start, then down, then left and through the really small spike-lined passage. That glyph over there gives you exposition when you sonar it, which I assume is the reason why it was ruled out, but it also acts as a key. Weird.
It'd be really awesome if someone started TASing this game again. I have no doubt there's more stuff yet to find. This game is broken as hell; we just don't know the particulars yet.
Good luck!