According to a report from Neowin, it is looking as though Microsoft could be bringing Windows 10 Redstone 5 builds to Skip Ahead Windows Insiders soon. This is coming from a statement made during the most recent Windows Insider Webcast but also occurs right as Microsoft is running the only Bug Bash for Redstone 4.
Specifically, Microsoft apparently confirmed in the webcast that Redstone 5 builds would be coming "sooner than you think." Though shocking for some, this is not much of a surprise for long-time Windows Insiders. The reason why? At the end of development of the previous Redstone 3 (RS3) release, Microsoft created (but limited and later closed enrollment) in the Skip Ahead ring so Windows Insiders could get a preview of Redstone 4 before it reached the Fast Ring.
— BuildFeed (@buildfeed) February 6, 2018
In addition to Microsoft's comments, the tweet from BuildFeed above also shows that Redstone 5 is already in development and has been compiled. Plus, with Microsoft saying Redstone 4 would only be seeing one Bug Bash, it definitely looks as though Microsoft is looking to shift their attention and release Redstone 5 previews soon.
Unfortunately, Microsoft also confirmed in the webcast that Skip Ahead is at capacity, so new Windows Insiders looking to join the Skip Ahead ring won't be able to jump on this Redstone 5 builds just yet. As always it is best to keep tuned for more information as this story is likely to develop over the next few weeks.