To be able to mark rules as backward chaining would be useful.
The consecuences of bc rules are added to the forward chaining network. They are matched against premises, and when they match, the prem is marked with a reference to the bc rule.
When a fact is added, it goes through the fc network, match premises, combine with previous matches. Here, bc consecuences act like previous matches. (Pre)activation of a rule with the help of a consec from a bc rule triggers a test for the premises of the bc rule.
How much of a performance penalty?