Re: custom modules. One (arguably) interesting thing we do is to only take the MAXIMUM subscore of all 7 topics and use that component in the composite score, ignoring the other 6 topics. This allows candidates to focus on only certain topics if they want. Employers want someone who is strong in one area, rather than a jack-of-all trades and master of none.
Adaptive testing (https://en.wikipedia.org/wiki/Computerized_adaptive_testing) is something we're looking into, and would be extremely interesting (and challenging!) to build.