Taking a step back: one of the larger changes for this driver was to remove all of the hard coded defines for an Icarus-based driver's read-size and to instead specify it on the Icarus info struct. That is the basis of making the AntMiner U1 work.

What you are suggesting is essentially a step backwords: to go back to using hard-coded defines to specify a driver's read-size. In addition, the value for Cairnsmore (4) is already in the code once. So what you are suggesting is defining the read-size of Cairnsmore twice in code in two separate locations, which could lead to bugs in the future.