[2024] Took me a while to grind to grind this, only to find out it still doesn't work at all. Is it reasonable to expect it to be fixed for 1.0? Hasn't been working since at least early last year.

It's been fixed internally and that fix will be included in 1.0. The problem was that before 1.0, not all the sufficient data for skill casting restrictions was synced to the client, so although the server would have let you use Lunge without a target, the client was still applying the skill's default targeting restrictions.

It does, I'm afraid. The client correctly recognises that you can't use Serpent Strike without a spear, and won't try to play an animation for it.