I've just created new extension for mediawiki. This extension creates a new handler for three new tags :<ncbigene/> , <ncbisnp> and <ncbipubmed>.
Each of those tags download asynchronously a XML record from the NCBI (Gene, NCBI Pubmed or dbSNP) using NCBI-EFetch. The XML is then transformed to HTML on the client side using a XSLT transformation and inserted in the mediawiki page. (As the XSLT processor is specific from Firefox I'm afraid this extension won't run for the other browsers ). As I'm using XSLT, the stylesheets are easily modifiable and hence, the HTML rendering is truly customizable.
The source code is available on github: http://github.com/lindenb/mw4bio/
The installation was described on Mediawiki.org: http://www.mediawiki.org/wiki/Extension:Mwncbi.