{%%} syntax looks really "wiki-like". That's a kind of reverse logic, comparing to MediaWiki, where parser functions are converted to HTML output, not opposite. What's really important, parser functions can be nested (and by using proper parser frame parser tags probably can be nested as well - I haven't tried that yet but might try soon). Can LocalWiki template tags be nested as well?
The template tags can be nested, yeah. Chaining in templates is usually achived using template filters, though, a'la https://docs.djangoproject.com/en/dev/ref/templates/builtins/?from=olddocs#s....
Our goal with the template representation stuff was to leverage as much of the existing Django ecosystem as possible. For instance, we were able to use a common thumbnailing template tag library without modification. But in general, if you want dynamic bits in pieces inside of a serializable/cachable mostly-HTML document, a Django template kinda makes sense.
We'll likely kill off the explicit {% .. %} syntax and build the template tree manually in order to simplify the process of writing page plugins.
--Philip