Have read this in Google Android-Developer Answer in the thread linked by Erel:
"Persistent identifiers are still available because there are various supported use cases which aren’t related to advertising."
See "Targeting devices without an advertising ID"
Seems you still can use Android_Id depending on use-case.
Very interesting for me as I´m developing an APP for devices not necessary connected to internet.
Also, I´m not wanting to use adds in my APP.