Constantly attaching new features and working around existing users is just what online games do, the pretence that it's an "Alpha" phase that will someday move into a "Beta" phase when some arbitrary amount of stability has been reached is a fallacy. Game is released and it is what it is, and people sadly paid for it.
Yes, when it comes to online games, and for example rolling release software alpha, beta terms have little different meaning compared to traditional software. Technically on traditional terms everyone of them would be in "alpha state" untill game starts dying and does not get any new feature updates anymore.
Traditionally:
Alpha = It runs, is not fully feature complete, very likely has big collection of bugs...
Beta = Feature complete, needs some bug smashing.
Release = Its ready now, will not get any features, at most some security and bug removal updates.
It seems more and more to me that CIG and its defenders use "alpha" as an excuse for poor quality. Lets call SC honestly what it is. It is a rolling release released online game. Just with macrotransactions and poor quality.