In this question someone suggested that the classic 'elf' ear could evolve for the same use as whiskers. How (un)realistic is this idea. Lets assume that the humanoid species that evolved these ears evolved in jungles. Would long ears be a reasonable tool for whisker use?
To add to SJuan76 answer, cats are animals that are frequently crawling into holes and tight areas in order to catch rats and the like. The other functionnality of whiskers is to check if the cat's body will be able to pass through a tight space before the entire cat engage.
To make use of that functionnality, human ears would need to be as large as shoulders. But even then, we humans can try to pass through a tight spot and make a step backward if we don't fit, since we don't have a long body behind us to manoeuver. Plus, if we don't fit, we can just turn and side step our way.
So half the usage of whiskers is lost to humans. Seems pretty unrealistic to me. If you combine the tight space navigation with the bad view complement, long whisker-ears seem more usefull to dwarves than elves.
The main issue with the idea is that, for whiskers to be useful, you need that your sight is not. Given that the eyes give way more information than whiskers, it seems like a great leap backwards.
Whiskers are useful only when visibility is low or impossible (cats, dogs and the like have horrible vision); humans would lose the advantages of superior sight in those situations so they would avoid them (lighting fires at night, for example). And, once the humans can use sight, whiskers become useless.
Additionally, two issues with "ears as whiskers" design:
Ears are way heavier than whiskers. They are also sensitive, and can be infected. Not something you want to use to check if the floor is full of broken glass.
Ears are located in the middle of the head, so it is highly probable that you will "feel" threats with your face before you can tell them with your ears. Note that animal whiskers are placed as forward as possible.