Currently the note says:
"A consistent format should be adopted "
I would suggest, given recent discussions (2010-10-13) on TEI-L that at very least we might want to clarify the distinction between 'free' and 'restricted'. (Even though, I note, the example does this perfectly clearly, people are still confused about it.)
A couple options:
1) Perhaps rephrase the note along the lines of:
"If encoding multiple resources a consistent format for availability information should be adopted. The status attribute should be used to differentiate between resources entirely in the public domain and those with any form of IPR restriction (such as a particular license)."
2) Change the attribute values (open/closed, free/restricted/licensed, and other suggestions have all been made.)
It would be good to re-examine <availability> in light of developments in Rights Expression Languages to see if:
a) TEI wishes to recommend some specific XML-based language in its own namespace
b) TEI wishes to create its own general-purpose Rights Expression module
c) TEI wishes to add @target to <availability> to give a defined way to point to a machine-readable expression of rights (in whatever format)
d) TEI wishes definitely not to do none of these and leave <availability>'s content as model.pLike