When writing your own transducers, there are some procedures that are good to have. There are a bunch of [collection]-reduce functions that are useful when writing procedures that expand one value to many values (like tcat/tconcatenate or tflatten) or when you accumulate values and have to finalize them (like tsegment or tpartition). They are however _not_ very useful when you just want to use the transducers. Likewise, there are functions to deal with reducing and unreducing values (meaning: telling the reduction to stop and helper functions for the transducers described above).
I would put the transducers themselves into (srfi 171) and the ones used to write transducers into (srfi 171 meta). That way, people who just want to use existing transducers can import (srfi 171) and those who want to write their own can import both.
Sorry about the delay, I have spent a majority of my vacation being ill.
That seems to always be the way of it.