The Windows Phones eligible to get Windows 10 Mobile Creators Update:
Alcatel IDOL 4S
Alcatel OneTouch Fierce XL
HP Elite x3
Lenovo Softbank 503LV
MCJ Madosma Q601
Microsoft Lumia 550
Microsoft Lumia 640/640XL
Microsoft Lumia 650
Microsoft Lumia 950/950 XL
Trinity NuAns Neo
Microsoft has been releasing early preview builds of the next feature update for Windows 10, codenamed "Redstone 3," to PC testers in the Fast Ring. The company has also released something called "Feature 2" (builds in the 15200 series) to Insiders running the handful of Windows Phones that are eligible to get the Creators Update RTM.
My -- and other Microsoft watchers' guess -- is that Microsoft plans to make its upcoming Windows 10 on ARM version of the operating system its future mobile OS platform. Windows 10 Mobile will likely continue to be supported for some period of time, as Microsoft is continuing to market it to specific vertical markets.
As company officials said previously, Microsoft is taking a phased approach to the Creators Update rollout and repeated again that only tech-savvy users attempt to proactively download the final Creators Update bits. Microsoft's guidance is to wait for the company to push Creators Update to devices via Windows Update to minimize possible compatibility and other issues.
The Windows 10 Mobile Creators Update release includes only a subset of the features that are in the PC version. A list of some of the new more business-focused features in the Mobile release -- including SD card encryption, remote PIN resets for Azure Active Directory accounts, WiFi Direct Management, and a few more -- are in this Microsoft article on IT pro content in version 1703, aka the Creators Update. (Thanks to @WinObs for the link.)