Hi sachsm,
I was told initially that it is a performance issue, but after doing some extra research I have found that it cannot be the case. You are right that the cRIOs that have the LX25 and LX45 FPGAs support the scan engine, so the answer lies outside the bounds of performance requirements. I spoke with some of our more senior engineers, who believe that R&D has phased out scan engine support for the newer sbRIOs based on the majority use cases for which they are deployed. Notice on the product pages for these devices that only OEM quantities are available for purchase, meaning that most of our customers for these are companies producing many units, and who generally desire to use the FPGA interface (not the Scan Interface). Each sbRIO that currently supports the Scan Interface (older models) has a custom scan engine bitfile that is written to the FPGA, and I guess someone on the development side of things decided that it wasn't worth the effort to write scan engine bitfiles for these new models. There is no indication that these will be supported by the scan interface in the future.
cRIO, on the other hand, is intended to have custom and reconfigurable module setups, and thus will always require the scan engine for those who wish to use the real-time functionality without having to deal with the FPGA interface.
I hope that this clears up some of the confusion!
