This IS something I thought of myself, but I can't imagine I'm the only one. However, it was met with "OMFG GENIUS!" over on Twitter, so I'll share it with you.
This solves all the worries about darned in ends pulling loose again. And since it's a felting needle, it MECHANICALLY smashes the fibers together, so it can felt/snarl together ANY fibers, even 30% nylon like above, or even pure silk.
I got these at my LYS, Natural Stitches, but I've seen them at JoAnn Fabric, and I'm sure someone sells them mail order.
Enjoy your darned in ends!
For your amusement, a You Tube video of the manufacture of steel wool. It's needle felted. (The needle felting starts around 4:15.)