Great question is one that's definitely asked annually with each Apple release.
As with any major OS release, whether it be Windows or Mac, best practice is to avoid updating for 3 months (minimum) to avoid any potential pitfalls, be it drive recognition issues or compatibility problems.
While it may be RC labeled, it still has yet to be have gone "gold." In other words, there could still be source code changes to fix defects, changes to data files, etc., all which could create potential problems for DJ's and producers alike.
While new Macs will certainly come pre-loaded, the 2k16 MBP's won't be dropping for a bit longer–hopefully all OS related issues will be squashed by that time.
If you do insist on tempting fate, definitely perform a full Time Machine backup prior to doing so in case you encounter any problems. Personally, I perform a Time Machine backup and fresh install when updating my OS. That's just me. :-)
While I don't work for Pioneer, I would assume they've been testing Sierra, but may want until the RTM/gold release to address any significant problems since Beta/RC can still experience changes. @Pulse or @Mark may have a bit more insight.
Cheers.
