Per early interviews and 10ftC, Chris' view of "beta" is: Everything is complete and in the game, it is ready from creator/dev standpoint. It just needs a HARD shakedown, and follow-on fixes, by the vicious users/players.
That's kind of a classic programmers view of "beta".
Now, while his views may have evolved a little bit with the years of experience of iterative, player interactive development, the time elapsed, and the sheer size that SC has grown to, we have to assume that is still his underlying core view of when you call something "the beta release".
That argues that the beta release will:
A) come VERY late in development, after we have seen "playable alphas" of multi-system play, large battles, insurance claims and replacement, multi-character and employee play, economy driven trade, etc, etc. And also seen the integration of most of those systems in preceding alphas.
B) be comparatively short, maybe a month or two. Followed by a relatively limited fix period (? 2 months ?), and a second short beta (? mere weeks ?), time allowed for final critical hot fix (? 2 weeks ?), enormous fanfare and hype, and "final" live release.
Then I would expect the first hot patch in about a month, 2-3 more hot patches over several succeeding months, and an update release in about a year.
All that having been said, "When for the initial declared beta?"
= Sometime in 2022 ?? Maybe as late as 2nd Q 2023 ?? =
I suspect that Chris would very much prefer that development-to-beta NOT stretch into a 2nd decade.