Scary Transclusion is not going to be enabled anytime soon at WMF, if ever.
However, it is possible to fake cross-domains transclusion using
javascript.
I wrote a set of javascript functions that do this, using the new API.
You can see it working on la.ws.
It uses a template that transcludes a single page from another domain.
http://la.wikisource.org/wiki/Usor:ThomasV/test
http://la.wikisource.org/wiki/Usor:ThomasV/test3
As you can see, the template inserts blank lines between pages, so it is
not
appropriate if you want to transclude many pages. Here is another template
that transcludes many pages using the 'pages' syntax :
http://la.wikisource.org/wiki/Usor:ThomasV/test2
These templates should work on all subdomains that call the the OCR.js
page at
ws.org
ThomasV