When all your AP's work in bridge mode then it's hard to identify the origin of Hotspot users. E.g. from which specific AP the clients are connected through. Creating a vlan for each AP is a very cumbersome approach when you deal with many AP's.
In RouterOS the PPP can forward the circuit-id received from the NAS to the Radius server using the NAS-Port-Id attribute.
/ppp aaa set use-circuit-id-in-nas-port-id=yes
It would be tremendous feature to enable circuit-id option as well in the Hotspot Service Profile under Radius.
/hotspot profile set use-circuit-id-in-nas-port-id=yes
When using DHCP then Circuit-Id and Remote-Id are available from leases via Option 82. If this value is not retrieved then just keep the default value of interface name.