One suggestion I've made is to add some additional syntactic sugar for templates.  Something like:

{{>Template}}

foo

{{<Template}}

which would pass all the content between {{>Template}} and {{<Template}} as a single parameter.  This would work around all the splitting/escape issues and allow us to rewrite {{table-start}} / {{table-end}} template pairs as {{>table}} / {{<table}} -- ie, minimal changes to to the wikitext would be required, but the result would be a properly nested template invocation.  (This idea is stolen from http://handlebarsjs.com/ .)

This is still highly speculative, but I'm interested in discussion.

 --scott