This is good news, in an email from TfL:

(It doesn't say if the card has to be registered though, perhaps that's
what the "may" is implying?).

"If you have an Oyster Card you no longer need, you may be able to get a
refund for it at our improved ticket machines in Tube stations.

You can get a refund at ticket machines for up to £10 of pay as you go
credit and your deposit."
--
Roland Perry