It sounds like you & a lot of the community are looking for promised, guaranteed, absolutely reliable delivery dates for production CI4. I can proudly announce the following guarantees, and I will publically eat a baseball cap if we do not meet them.
Alpha - No later than ... 2018
Beta - No later than ... 2019
RC - No later than ... 2020
Release - No later than ... 2021
Seriously, what you ask is impossible. This is a community developed framework, not a corporate enterprise with a reasonable sized full-time team. If you look at the contributors on github, the list is pretty short, with a handful able to contribute significantly. We all have day jobs, and lives outside of that and CI. The way to move forward the release dates is to get more involved in the development
The problem with "ballpark figures" or best guesses, is that readers overlook the word "guess" and mentally substitute the word "promise". I think Lonnie is bang on with his suggestion that Spring 2017 is what we are working to, but that target may or not be reasonable.
CodeIgniter 4 is not production ready. We encourage the community to play with it, report problems, make suggestions, and contribute the small or big bits that they can. There are a number of "issues" on github that are tagged as "help wanted", i.e. opportunities to kick in. As more features get sorted out, they will be added as new issues, to give the community an opportunity to work on them!
If you have a big project, I suggest sticking with CodeIgniter 3 for it.
If you have a small project, it might be an idea to try to build it using CodeIgniter 4, and let us know what works and what doesn't, or even better, to fix/add the pieces that are broken/missing