[1.2.279] Skill nerfs this time

If what you are suggesting is just jump casting, like what archers do, then it would make no difference in the range of the skill.
It would count as if you cast it from the ground where you were.

This was possible for a very long time, possibly from the beginning. I think people just didn't use it because its hard to do using Ultimate key alone without putting it in macro. Its very simple when you add the ultimate into a macro (just need to put it in once) and jump atk, you can do it 100% of the time. Without macro you'll have to do it at a perfect time, i've tried this way but its not worth that much effort to hit a few extra monsters. This is how you hit bottom 3 platforms of skele mini dungeon

I believe this buddy implies the macro's property of "register and cast immediately when possible."
If you played a Warrior, you'll notice that Rush does not register when in mid-air, but a macro'ed Rush does, hence you slide away as soon as you touch the ground. Same for Combat Step, really helpful when paired with the sliding motion + non-directional jumps.
So I'm assuming jump-ult means registering the ultimate when in mid-air (thus able to hit both plats) but the animation gets cast upon landing.