The reality of Reporting Services and AlwaysOn Availability Groups, is that Reporting Services lives on a server and points to a writable copy of ReportServer database. Having the ReportServer database in the AG gives it the ability to failover to the secondaries. The other reality is that the secondary cannot be written to, so you really cannot point the Reporting Services to the secondary to write.
So the option you have is to point the Reporting Services to the AG Listener so that if the AG fails over the Reporting Services still continue to work and keeps it highly available. The challenge will be if you reboot the Primary Server the reporting services will stop until it is rebooted completely. You could do a scaleout Reporting Services implementation if you wanted to.
Only the databases that are used in reports can use ApplicationIntent=ReadOnly in the connection string to leverage the readable secondaries.