There are a couple of problems with microchipping. The cost is one - those RFID chips and readers are not cheap. The second (and biggest, IMO) is how does someone who is not a quilter know there is a microchip in the quilt?
I still like the QR code best. You can quilt the QR code right into the quilt, so that to remove it would mean destroying the quilt. Generating a code is free and very easy. Reading one does not take special equipment, only a smart phone.
My friend Cindi did a ton of research and wrote about QR codes, how to generate them, how to put them on a quilt. You can read about it here:
http://www.seamstobeyouandme.com/wor...des-on-quilts/
However, I don't believe someone stole all 4 of those missing quilts. It would be really, really hard to get all of them moved without attracting attention. I'm pretty sure there's a box somewhere with those quilts in it.