If you read through all the comments on the Indiegogo site, you will note that RAW output was not originally part of the offering, but they added it by customer request. At first try they could not get RAW output working with RTKLIB from VENUS 822 so they were going to use an older VENUS 6 chipset as the backup plan, which they stated upfront. Later you will note that they did report success with RTKLIB from the Venus 8 family, so after that there was no hardware limitation in place for Arduino programmability, so what happened then?
I don't know but it's easy to imagine there was some company meeting and the marketing-strategy people ruled out programmability for the RAW output version. Logically enough, because if it's just provided as library, you could buy the less expensive basic unit and simply reprogram it to be the (slightly) more expensive RAW one. The fact that Oliver posted the point about market segmentation on page himself, suggests to me he's not trying to hide what's going on. I can hardly criticize this strategy when it still ends up the cheapest raw-output GPS I'm aware of.
Compare that with the other vendors in the GPS space who do the same thing, but without actually saying it. In days gone by, the SiRF-Star II GPS chipset had an undocumented feature providing raw pseudorange and carrier phase. This was removed in SiRF-Star III, allegedly for this reason.
With the 10-nsec resolution I was also thinking about GPSDO. I note they have a 24-bit PWM which when filtered might be useful as a DC control signal as well; so it's possible you might get it to work without needing a separate controller.