One caveat on this change. I had to add
# Default Xinha Instance
set rich_text_spec {richtext(richtext),nospell,optional
{label Content}
{html {style {width: 100%}}}
{javascript {xinha_config.script_dir = 'wiki'}}
{options....}
}}}
set widget_specs [list *,text $rich_text_spec]
to the root object to get the Xinha to work for the non-plain pages.