It looks like the cat is out of the bag as far as the mystery surrounding the naming for the next update for Windows 10 is concerned. It appears that the "Creators Update" naming, first used a year ago, will be kept, with the full name ending up as Windows 10 Spring Creators Update, for Redstone 4.
The Spring Creators Update name has appeared numerous times in announcements, or as in the case above, in Powershell on Redstone 5, it will be the third time it has been used after the Creators Update, released in March 2017 and the Fall Creators Update, released in October last year. Annoyingly, it was expected that Windows Developer Day would be used to officially announce the name, but that came and went, although a new Windows SDK was released for developers.
Redstone 4, or as it is now known, the Windows 10 Spring Creators Update, will bring with it new features like Timeline, HDR support, and even more Fluent Design changes when it is released in April.
Source: Pennybridge1969 (Twitter) via The Verge