The workflow that wp core init-tests command encourages is the following:

• clone https://github.com/WordPress/WordPress
• run wp core init-tests

These days, if you're serious about doing Core development, you'll check out http://develop.svn.wordpress.org which contains not only the test suite, but other tools, like Grunt tasks.

So, the test suite is both more visible and easier to set up than before, which eliminates this command's raison d'etre. Therefore, it should be removed from WP-CLI.

One might argue that the command could be adapted so that it doesn't download the test suite, but simply configures the one that's downloaded from develop.svn.wordpress.org. The steps performed would be:

• create wp-tests-config.php
• create an empty database

However, neither require any WP-CLI machinery, so they could be automated just as easily with a plain bash or PHP script. (Or, ideally, added as a Grunt task to Core.)

FWIW, you may want to update http://wp-cli.org/blog/plugin-unit-tests.html since it references a now obsolete workflow. Not sure if you have a procedure in place for handling some of the old blog posts that now show irrelevant commands/info.

I'm probably going to write a new post and link to it from the old one.