Further, I'm not sure how I would create a stylesheet to do a transclusion. I have no argument with any of this. I think that the inclusion problem should be solved. I volunteer to be on a working group that sets out to solve it. Furthermore, the fact that XML would be handled differently from node-less data types would be another bizarre special case.
Inclusion is meaningful in contexts where there is no visual display.
If you want standardized node inclusion, I urge you to ask the W3C for it. But don't ask for the maintenance of a feature that cannot and was not intended to be node inclusion. Personally I would ask for that infrastructure before I would ask for the node inclusion. For starters, I think that we need a way of addresssing into the results transformations. The ISO grove model gives you the latter and the former is probably best represented as an extension to the query language shared by XSL and XPointer.