It'd be nice if using spacebar to ascend ladders and in particular scaffolding disabled the speed-boost given depending on the angle you look up and down. Because it becomes quite dangerous on scaffolding when ascending pressing spacebar and pressing forward, but also, I usually like to enjoy the view looking slightly down when ascending scaffolding.

It seems useful to at least be able to ascend quickly, is there a situation on scaffolding where pressing forward is required?

It's been many months since I played modded MC last, but as I recall it you needed to press forward to get the faster ladder climbing effect at all, but that becomes quite dangerous very quickly. Besides that, no, not when going straight up there's no use for pressing forward. But I guess I see a problem, because you can also move horizontally while inside scaffolding, and there you'd need to press forward. So it doesn't seem like a simple check of whether forward is pressed while climbing to give speed boost as that would make horizontal travel quite dangerous.
I can see how my request is hard to implement now..

I don't use scaffolding a ton, so I'm curious about the use case.

A quick test on 1.20 and 1.21 seems like shift/space for ascend/descend on scaffolding is unaffected by the speed boost. It does appear to boost like you said if you use the scaffold like a ladder, but is that seems to be solved by just not pressing forward?

It seems useful to at least be able to ascend quickly, is there a situation on scaffolding where pressing forward is required?