Interesting questions.
The quick answer is yes, JApplicationCli is what you'd use to build
the Joomla equivalent to Drush, but I probably wouldn't design Joosh
(?) like Drush.
What we are doing at eBay, for a project, is designing a web services
platform for next-gen sites, but we have a command line interface for
that platform as well. For example, the let's say the API for getting
an article (as a json string) is:
http:://api.url/article/123
We've made it so you can invoke that from the command line as well, like this:
$ services /v1/json/article/123
Where "v1" is the API version and "json" is the return format. The
CLI is just a proxy to the same/similar route to load the same
controller that the web service would load (two birds with one stone).
That's what I'd do if I was designing a new project or thinking about
the future of Joomla as a content delivery platform. As for
retrofitting the existing CMS with a CLI goes, that would be a big
job.
Regards,
Andrew Eddie