Did we need a new one to do this? Absolutely none of the hundreds of existing languages could have possibly worked, so let's reinvent SSI with different syntax?
Or someone should write an SSI static site generator.
Edit: Although what would be really nice would be the same kind of pre-processor that works with apache ssi directives
I'm sorry, but this project feels more like "art" than a practical tool.
Plus, with a few basic lines of PHP (available on every shared host) you can pre-generate your site statically as well (and on the server, to save you the re-uploading).
You should automate that with Grunt or Gulp. Static .html pages is best practise these days instead of dynamic templating.
Or you could just, y'know, run the static site generator on the server. What Linux doesn't have Python installed?
http://httpd.apache.org/docs/2.2/mod/mod_disk_cache.html
re:edit hxincl uses a similar style as ssi but with a couple of enhancements:
http://manpages.ubuntu.com/manpages/trusty/en/man1/hxincl.1....
if you want exactly SSI syntax, ain't nuthin' stopping you from pointing curl at localhost.