Are circular buffers relevant to transposed direct form IIR filters?
Circular buffers are only useful if the contents of the delay elements are not changed when shifted. So you're right that circular buffers cannot be used for the transposed structures. However, this doesn't necessarily mean that the transposed structures are less efficient than the direct forms, it just means that the data aren't just shifted through a delay line. The complexity for computing the new state vector in the transposed structure is comparable to the complexity for computing the output from the states in the direct form.