Bob,
Can you point to some XSL implementations in other programs (preferrably the good ones) so that we can see what some other applications are doing? This will help us better understand what you're looking for.
If adding the support you request isn't too difficult (for instance using our already existing XML parser to do some functions), we may be able to get it in soon. However if new custom controls need to be written for it, then prioritywise it probably will be placed behind some more database interactivity features that we're currently working on.