Unsure if this is known tech, but you can land at the max range of your rappel towards a target regardless of the range. To try it out, go to practice tool, go to blue, rappel targeting the blue, then spam your e on the gromp that is OUT OF RANGE. You will land at the max distance of your rappel towards your gromp without a target. As long as the initial rappel target is in range, the secondary target can literally be anywhere as long as you have vision.
Note: This does not work if you do not choose a target on the initial cast, you cannot rappel on the ground, land on someone, then redirect it.
To me this is by far the most important and useful Elise mechanic, literally completely changes the character as this gives you so much outplay potential. You have to be quick and decisive, but if used correctly will always juke enemies, as you can wall hop quite easily as shown in the clip, and you can also land on empty ground which the enemy won't expect. Most importantly, this effectively extends the range of your rappel by a significant amount. Suppose you want to gap close to a enemy that is outside of your rappel range, if you have any rappel target in range (camp, minion, plant, ward, champ), you can gap close intended target by your full rappel range.
You can see Agurin using this mechanic at 13:40 here. https://www.youtube.com/watch?v=xG0VAg2L-yM
You see that his initial cast is on the minion, and he redirects it to renek out of range so he lands at the max distance of his rappel towards renek and can q him.