Provide an plain old java alternative to score calculations, so the user has choice (= freedom):

• A) Drools score calculation (default). Does incremental calculation automatically, without extra code.
• B) Java non-incremental score calculation. Very easy to reuse existing score code, but not fast.
• C) Java incremental score calculation. Requires incremental boilerplate code, but experiments show that in some use cases (with little rules) it can be a 100 times faster than A) with drools 5.3. Note that undo-then and JIT compiling might change that number drastically in future drools versions.

Technically, it's a matter of overwriting SolutionDirector. For C) we'll also need to adjust the Move and ProblemFactChange interface accordingly.