Is it possible to add Radius Server (based on FreeRadius for example) as additional package? That will be very useful, I think. Especialy if this radius will work with exernal databases. Because MT box working extreamly stability on good hardware, it will be very good radius server solution.
We already have Radius server. Install the user manager package. For more info look on wiki:
http://wiki.mikrotik.com/wiki/User_Manager
Yes, of course, I now about UserManager. But I told about exactly Radius server as functional, with access to external databases. For example, I want to have few numbers PPPoE concentrators, and some DialUP server (Cisco for example) with centralized radius server on MT box, and ONE subscribers database with billing info. Yes, I can setup some linux box and install FreeRadius, but I like MT very much as quick, easy-to-confugure, very-sability (dream-come-true 
) solution, and having Mikrotik Radius Server will be the best choise.
user manager is the only choice for you now. maybe we will make external database export and other features