It's in the doc you posted. It must be an asset that can be stored on a us centralised exchange. For the duration of the loan I'd imagine.
Discussion
the amending of the Fannie Mae guide is the signal that this order pushes. The part about centralized exchange will and can be negotiated away. I’m trying, man
If you want a loan, I really don't think you can avoid giving up custody of your coin. It has to be seizable by the loan issuer.