Make sure that layout/template parameters can be "some/sub/directory/layout" or "toto/titi.html"
Using directory name in layout and template names would make it possible for the template designer to create his own packs and tidy up templates.
#5 for the "template" parameter.
Pretty useful if a project uses a lot of forms.
This would add extra flexibility.
WARNING: currently, the form.html and field_list.html templates are at layout root. So there could be a problem if the template designer want to use something like "fields/default.html" or "labels/default.html" as template names.