Revit Sundial by now, the cloud-based, hosted release preview that "provides a sneak peek into potential future enhancements for architects and MEP and structural engineers. With more than 35 features and enhancements to try, the preview includes Solon integration for more personalized building performance analysis, sequencing for power circuits, and enhanced rebar tools."
You may have also read that this release preview heralded the return of the Inside the Factory blog, following an over 2 year hiatus.
To this point, thinking that Revit Sundial was simply a preview of Revit 2016 (!), I've been quite content to sit back and watch my esteemed blogger colleagues' post about Revit Sundial. What's especially interesting to me though is that when one clicks the What's New link on Inside the Factory, Revit 2015 Help is opened! What is then described is a "Revit 2015 Subscription Advantage" release, with Revit Sundial being a preview of features that are being considering for a future subscription release.
While I have no inside information on the matter, it seems that Autodesk subscription customers may be in store for a mid-model year Revit release (I don't know if subscriber-only full-on product releases are common from Autodesk, but there is certainly precedent from competing vendors like Bentley Systems). Alternatively, some features may be rolled out as subscription enhancements, which puts this topic in the purview of Revit Add-ons. Again though, I have nothing to base this on, other than what I've already stated.
Mark this one as developing, and stay tuned. :)
What's New in Revit Sundial (AKA "What's New in Revit 2015 Subscription Advantage")
Inside the Factory (for Revit Sundial updates and information)
You might also be interested in: Project Solon: Building Performance Dashboards for Revit