I happened to stumble upon your question again after I recently came across
an interesting article describing implications for a model for a
stand-off annotation system based on XQuery
(<>). The authors have
experimented with MonetDB, which apparently implements specific XQuery
extensions for efficient querying of information distributed over documents
encoded in stand-off fashion
On their website, references to more papers can be found at

I don't have any experience / interest in this software, but was merely
excited to see XQuery being considered a valuable option for such kinds of
complex search problems (in this case natural language processing). I
realise this is probably a rather late reply and not very helpful to you in
the short run, but maybe it's worth remembering later?

> Your help in locating stand-off-TEI tools and projects will be
> gratefully appreciated and... wikified in due time, so that others can
> benefit from this as well.

Do you have a list already? Would be very interesting, I think.

Kind regards,