Support for <?xml-stylesheet to use Mallard in XHP?

So, I went on this ditzy sidequest of writing some help pages for an UNO
plugin. Like most extension authors, I didn't feel enticed by XHP
initially; and went with Mallard here.
Now I'm wondering if the LO helpviewer can be made to recognize an
embedded stylesheet reference:

  <?xml-stylesheet href="./mallard2xhp.xsl" type="text/xsl"?>
 
Haven't really looked this up, but I'd assume it strips out any such PIs
in favour of main_transform.xsl. Or libxslt discards it by itself when
fed an override?
Or is it just due to the relative path? (Is %origin%/… supposed to work
in this context?)

Else, couldn't the helpviewer support more than one file type? As in
preconvert *.page files itself? The formats are close enough for some
crude mapping:
  http://fossil.include-once.org/pagetranslate/artifact/4597b7ac
Fully converting <link> to <bookmark> absolute path references would
be a bit more involving, of course. But doesn't seem totally infeasible.
(Crossposting to @projectmallard, to lure some feedback.)

Presumably there's zero demand to migrate the Open/LibreOffice help
system at large. But you know, the documentation prevalence among
extensions is a bit lower. Not sure if it's just me, or if any such
effort would be warranted there.