High level requirements have been documented at:
https://mifosforge.jira.com/wiki/display/projects/Business+Rules+Engine
Need the following to be document:
Are we ok to go with integration with Drools (if not which else)
approach of integrating - for example: extend the "listener" model which was implemented for the guarantor release functionality
approach on how data (client, accounts, transactions etc) from the calling code will be passed to a specific rule
approach for UI integration with Mifos X and with the tools UI for maintaining rules (it could even be that the UI will remain separate without any access for operational users and is meant to be used only by a specialist)
Rule change history maintenance