pfSense

AFAIK pfsense NAS recognizes the WISPr RADIUS attributes such as
WISPr-Bandwidth-Max-Up
WISPr-Bandwidth-Max-Down
In certain deployments it would be helpful to also have traffic limits.

Could consider adding custom RADIUS attributes, similar to what some other NAS provide e.g.

Chillispot http://www.chillispot.info/features.html
ChilliSpot-Max-Input-Octets Maximum number of octets the user is allowed to transmit. After this limit has been reached the user will be disconnected.
ChilliSpot-Max-Output-Octets Maximum number of octets the user is allowed to receive. After this limit has been reached the user will be disconnected.
ChilliSpot-Max-Total-Octets Maximum number of octets the user is allowed to transfer (sum of octets transmitted and received). After this limit has been reached the user will be disconnected.

Mikrotik http://wiki.mikrotik.com/wiki/Manual:RADIUS_Client
Mikrotik-Recv-Limit - total receive limit in bytes for the client
Mikrotik-Recv-Limit-Gigawords - 4G (2^32) bytes of total receive limit (bits 32..63, when bits 0..31 are delivered in Mikrotik-Recv-Limit)
Mikrotik-Xmit-Limit - total transmit limit in bytes for the client
Mikrotik-Xmit-Limit-Gigawords - 4G (2^32) bytes of total transmit limit (bits 32..63, when bits 0..31 are delivered in Mikrotik-Recv-Limit)

(Note: Various other examples are available in FreeRadius' dictionary directory)