Consider a language where even pretty 'simple' voices like reflexives and reciprocals are expressed using auxiliaries. This provides an interesting space for introducing the distinction between reciprocals and reflexives - number congruence!
If there is some form of person marking possible on infinitives as well, one could imagine having the infinitive take singular marking for reciprocals (or maybe vice versa); however, one could also imagine using just plural verb forms for plural reciprocal subjects, and singular verb forms for plural reflexive subjects.
What if we want the reflexivity or reciprocality not to be with regards to a direct object? Maybe the auxiliaries for voice can stack, and some of them give applicatives and circumstantial voices. Maybe the relevant case-marker (adposition, whatever) can be incorporated in the auxiliary, or turned into an argument of the verb?
I've been doing really gruelling work on the historical sound changes of Ćwarmin and Ŋʒädär, and will soon post some updates on those. Expect pretty detailed stuff.