Well, it's open source. Are there mysterious binary blobs that I'm not aware of? If not, then when this becomes Google's new mobile OS then it's going to be the same as the situation today with AOSP running a bunch of untrustworthy closed-source Google services and apps.
Fuchsia has different Open Source license. OEM don't have to make their modification opensource. So if you oem you can run any binary blob. Also you don't have to make drivers available.