Actually, I'm having trouble using {{template}}s as a workaround -- it's not correctly processing the {{{field}}}s specified in the template. The template is transcluded as:
 
{{{for template|RSS}}}{{Template: Form RSS}}{{{end template}}}
I had originally tried placing the {{{for template}}} & {{{end template}}} calls inside the {{template:Form RSS}} however Mediwaiki hung as soons as it prepared to switch to the AddData page. With those two calls outside the template, the result was that no input controls were displayed, rather the names of each of the fields were displayed!
 
Hope this helps. This moment, I don't see any workaround when there are common portions of a form. Neither transcluding subforms nor transcluding templates seems to do the trick. The result is that common fields need to be -copied- among all the forms that share them in common?
 
Thanks for any advice. 
-----Original Message-----
From: John McClure [mailto:jmcclure@hypergrove.com]
Sent: Tuesday, August 18, 2009 4:58 PM
To: semediawiki-user@lists.sourceforge.net
Subject: RE: [SF] Form transclusion - Mediawiki hangs

I'd like to transclude other forms in my form -- as 'subforms' -- but it's completely inoperable, and causes Mediawiki to hang. I do recognize the workaround, to create a template that contains the 'guts' of the sub-form. That's a chore to do with all forms. It should be easier to 'inherit forms' by a subcategory; a subcategory's default form merely should add those field(s) that specialize the subcategory.
 
Forms should be able to transclude other forms as templates can transclude other templates. Well, that's my opinion, but at least it shouldn't hang...
Thanks in advance - John