When will Drupal 8 be officially supported?
I've recently been reviewing the code, testing against Drupal 8.2.5, and developing and submitting Pull Requests to the D8 module. I've been roughly estimating the time that would be required to get it working good enough to install on a client's site. 

The core module has all the CiviCRM admin pages and menus working, albeit with some JavaScript errors occasionally. The install process could use a little work, and the profile integration on the user view and edit pages needs an overhaul. 

I think this all could be fixed up and QA with 40-120 hrs work to achieve a reasonable Minimum Viable Product(MVP) to release as an alpha version. That's a purposefully broad estimate, there's bound to be a few things to fix that remain unknown.

That being said, one organization with a decent budget that wants CiviCRM in D8 could have it, and make it happen for the rest of the community at the same time, there's definitely plenty that does work.

You can see the current installation procedure if you want to try it out in a related article:
Does CiviCRM work with Drupal 8 and how can I help?