Regular expressions are defined by referencing XML Schema, 
and XML Schema only supports XML 1.0.  XQuery, on the other hand,
permits but does not require support for XML 1.1.  The question is
whether regular expressions are impacted by XML 1.1.  My survey
indicates the following potential issues:

1. \c is defined in XML Schema as those characters matching NameChar.
The definition of NameChar changed from XML 1.0 to XML 1.1.
Does \c in XQuery use the XML 1.0 definition, or does it permit
an implementation to substitute the XML 1.1 definition?

2. \i is defined as "the set of initial name characters, 
those ·match·ed by Letter | '_' | ':' ".  So we have here two 
definitions, one notional and the other by explicit enumeration.
If you look in XML 1.1, Letter is not changed, but there is a 
new rule called NameStartChar which clearly corresponds to 
"the set of initial name characters".  I think that XML 1.1 users
will expect that \i matches NameStartChar rather than 
Letter | '_' | ':'.

It might also be useful to coordinate XQuery's response to this
with the XML Schema working group, in case they have plans to
upgrade their definition of regular expressions to align with 
XML 1.1.