What makes you think this is a hard concept? Its really quite simple on the surface. But like some things which seem simple, it has scope beyond the surface.They aren't pre-spending anything. They are committed to a course of movement based on what they've done. You can't really change direction mid-leap. No different than if they had leaped off a thousand foot cliff and were still falling at the end of their turn.
If on their turn the extra height of their leap allowed them to see their target square contained a trap that they hadn't seen before they still couldn't change where they were going to land. No difference.
I don't see why this is a hard concept.
The hangtime thing can create a lot of possibilities. I ready an action to shoot an enemy i can see and i run 15' and start a leap across the 30' gap and go into hangtime there over the gap 15' across.
During the round that follows enemies appear down below and my ready shot goes off.
Start of my ne t turn, i take that opportunity to use that turn attsck to shoot again as i complete the jump.
Two turns of shots during one "jump".
Thats a more active use thsn ssy the defensive "thwart hold person" kind of on i gave before.
As for the jargon...
If you prefer to use "comitting" as your label for getting your movement from next turn locked in now instead of "pre-spending" thats great. No problem.
Are there any other activities from next turn you allow player to pre... Errr... "commit" on previous turns so they still go off even if they would be unavailable? There may not be but i am curious since i dont have the experience with your house rule in 5e.
In HERO, for example, you could "call up" to dodge or block iirc as a reaction, losing your whole next turn but that was for reaction not during your turn.