This was my first thought after reading the release notes, but there are other changes in the firmware. Clearly, I don’t have a second Bartók available, so this is all I’ll be able to do, but it’s those other changes potential impact that made me think having a second Bartók would be what it takes to really A/B the changes. There were people discussing the impact of the last firmware update and dCS politely said they didn’t expect any audible differences in that set of changes.You won't need to; Mapper 2 is the original mapping algorithm, while Mapper 1 and 3 are the new algorithms. So, it's very easy to do A/B comparison by just selecting the appropriate mappers during playback. The differences is very clear, at least on the Vivaldi and Rossini currently, and I assume will be on the Bartok as well.
I’ve been doing a lot of reading about Rossini 2.0 and the similar rollout that occurred for Rossini in about January 2019. It very much looks the same in announcement, release notes, etc. Release day can’t get here fast enough.