@Kristine Naess I agree with you that opening up the parent/child capability for Business/Technical Services is another worthwhile discussion, in addition to parent/child Offerings.  Having both of these available does make it much more flexible to build out a portfolio that has the appropriate level of granularity to meet the needs that are ultimately dictated by the size, structure, and maturity of the company.  Choosing a rigid structure that doesn't allow for this flexibility is an impediment to adoption and that just doesn't seem like a good business choice.

That said, like you I have considered possibly extending the Taxonomy itself to try and compensate for this.  My thought was rather than using just Service Types and Service Categories from TBM, one could extend the Service itself to be a Taxonomy Level, which would allow you to (as needed) break down those Services by function/component/etc., as you would normally do at the Offering level, and then further break each down into separate Offerings.  But that seems like a hack that would introduce more cognitive dissonance than it would solve problems.