I could go either way on this, but I do think that multiples make sense for recommendations.  Module A does things B and C.  However, module X is better at B and Y is better at C.  Or, you want to give people options.  We can weight the suggestions by occurrence and order.  So, the user should prioritize the order of recommendations.  That doesn't really solve the problem that I've actually referred to here, but I don't see a need to limit this input to 1 item.