Basically, there are following plugins that provides HTML5 preview facilities:
- org.jboss.tools.vpe.preview - separate editor agnostic view with HTML5 support 
- org.jboss.tools.vpe.preview.editor - provides part with HTML5 preview to VPE.
- org.jboss.tools.vpe.preview.core - common code shared among *.preview and *.editor bundles.
Currently, org.jboss.tools.vpe.preview.core has dependency on org.jboss.tools.vpe.xulrunner for XulRunnerErrorWrapper class in order to process Xulrunner specific errors i.e. GTK / Xulrunner detection etc. So, it would be quite easy to remove this dependency from .core bundle in order to make HTML5 preview Xulrunner independent. However, .editor bundle already has dependency on org.jboss.tools.vpe (require xulrunner, xpcom etc.) and this dependence can not be removed. The only idea that comes to my mind is having two separate feature for HTML5 preview (no xulrunner dependency - can be included to rpm) and Visual Page Viewer (with xulrunner dependency).
 More details about HTML preview can be found in the following blog - http://tools.jboss.org/blog/2014-04-24-html-preview-is-taking-shape.html