From what I’ve understand, the tracking will be on the Google Play Services infrastructure. I believe that MicroG could choose to no apply it in theirs.
I read this article here: https://www.theverge.com/2020/4/10/21216484/google-apple-coronavirus-contract-tracing-bluetooth-location-tracking-data-app
It scared the hell out of me.
Securing the communication on Bluetooth? 
This is nothing but a joke.
Well, if anyone want to use it, fine with me, people should be allowed to choose but count me out!
If, and it’s a big if here, this monstruosity lands on /e/ I will have to rethink my choices, unfortunately.