Phil Roberts wrote a paper on Latin rhotacism, which was published in the Transactions of the Philological Society. The historical development of rhotacism he regards as a textbook example of the life cycle of a phonological generalisation: the domain it applies to progressively shrinks through the history of Latin.
The published version of Latin Rhotacism: A Case Study in the Life cycle of Phonological Processes
can be downloaded from the Wiley Online Library, a pre-press manuscript copy is available from Oxford Research Archive.