Compared to the present state of xml export for docbook there are only some minor (as far I looked into it) issues and then it will be ok for docbook5 at the first glance:
1: id should become xml:id
2: the firstname and surname should be encapsulated by personname.
3: ulink should be a link and uri should be encapsulated with xlink:href like
<link xlink:href="http://www.unboundmedicine.com/medline/citation/16252695/...">http://www.unboundmedicine.com/medline/citation/16252695/...</link> (... to make it readable)
4: More troublesome is the fact that the default pattern for bibtexkey generation [authshort][shortyear] which produces ABC+95 e.g. will not work with docbook. The plus sign is not allowed. It would be nice therefore if the bibtex/biblatex --> xml transformation would transform any ABC+95 to ABC.95 which is allowed and gives the same information that there are more authors to be.
5: A nice to have would be when the transformation would make the xreflabel=“Abel et al.(1995)” for ABC+95. But is maybe a to great wish.
6: To include fields like DOI would be also nice to have, since they appear in citation list and are by themselves links to the document in the internet.
My five Cents