There's recently been a bit of an argument about whether you should be able to duck-jump into gaps that you fall past on your way down. My position has been that if duck-jumping into crawlspaces is a thing at all, it should also work when you're falling past crawlspaces since that's consistent. However, there's another way to be consistent - not allow duck-jumping at all. CSD suggested that in Discord, and I can definitely see merit in that plan, since it puts more tools in the hands of level designers (and put the burden of not trapping the player in an area that requires duck jumping on them as well). In particular, tutorial level 2 is fairly poorly designed without duck-jumping since it's easy to trap yourself behind the steel crates if you trigger the second set of arrows too quickly, but that would be fairly simple to rectify by changing the level.

So what do you guys think? Would it be better to keep duck jumping in (with the ability to duck jump into any crawlspace) or would it be better to get rid of it entirely?

I would find it quite jarring if I couldn't duck-jump. I don't really use it to get into gaps, just to shorten my jump height. Controversial idea: make jump height relative to the time the jump button is held down. A lot of platformers do that these days. Exchanges simplicity/consistency for potential depth of physical skill.

Wouldn't be the same game at all if that were possible.

I say keep it, I'd rather have duck jumping and have to adapt for the fact you can get into small spaces (like I showed in that picture in the other thread) if it isn't possible to recitfy this than remove it entirely

keep it. It still makes traps possible and isn't so intricate, yet allows MUCH more complexity in levels.