It's a trend ...
Now I am old, you may not be, but to me it's a trend that you can't really undo if you decide it was a bad idea later on down the line and that it is awesome today but when you're 60 and your ear lobes begin to sag, this will just look hideous. And yes, you can un-stretch but it never does go back to normal, really.
Trend, yes. Irreversible, no.
The only time they won't grow over and shrink back to normal is if you go over the 00 gauge (10 millimeters). That's the point of no return. It is possible for them to shrink after that but it's rare and a very long process. It's not unlike other piercings though, if you don't go too far it can be reversed with little to no evidence of it ever existing.
For those who don't know what it actually looks like: