I looked at MicroG and saw this almost immediately: This is alpha-grade software and not yet ready for production use. Do not use if you don't know what you're doing.
That's not going to be good enough for Huawei.
Similarly, all of those alternative OSes aren't going to work if they're not binary, and more importantly API compatible with Android + GMS.
The question is rather: given that it is FOSS is it good enough for them to extend the functionality on the short-term?
> Similarly, all of those alternative OSes aren't going to work if they're not binary, and more importantly API compatible with Android + GMS.
KaiOS has some compatibility (by design not fully compatible).
SailfishOS has an Android emulator. Other OSes could also use one such as Anbox.
/e/ and LineageOS are binary and API compatible with Android.
GMS is an issue, but given that Google is under a magnifying glass concerning monopoly position related to Android in EU I have some hope that alternatives for GMS (or FOSS implementations) could happen.
That's not going to be good enough for Huawei.
Similarly, all of those alternative OSes aren't going to work if they're not binary, and more importantly API compatible with Android + GMS.