Absolute encoders have been around for some time, but NI's motion hardware still supports only incremental encoders. I would like to see support for absolute encoders in NI Motion or NI Soft Motion.
In NI SoftMotion, there are many examples where the FPGA code is user-accessible. It would be possible to add absolute encoder feedback there.
NI Motion is a closed black box, but SoftMotion has that flexibility. It would take a bit of work, but absolute encoders can vary so the customization would be needed either way. Also, they tend to work over BiSS (or synchronous serial "SSI) - we have partners that make C-series modules for that such as this: http://www.sea-gmbh.com/en/products/compactrio-products/interface-busses/sea-9521-bissssi/