(I reread ops question and I can only see the term open source 2 times, but whatever, I understand what you say, and I don't want to debate about semantics.)
The point with microG is it's still the best way if you want to use android. The other options are:
Play services (GMS), or Huawei has some similar solution because of US trade embragoes.
You can use android without play services but notifications won't work for most apps, even if you can open them. (UnifiedPush tries to solve notification part) Wifi and cell based location won't work
I see microG as an acceptable middle ground. I still have to give up something to goog, but it's not much compared to GMS, and I can use all available apps
(I reread ops question and I can only see the term open source 2 times, but whatever, I understand what you say, and I don't want to debate about semantics.)
The point with microG is it's still the best way if you want to use android. The other options are:
And maybe tomorrow we'll see UP grow up, removing one more piece from google. And the day after, another piece.