Microsoft may start shipping the first Windows 10 21H1 preview builds as soon as next month, according to a post from the DirectX Developer blog that has now been edited since its publication on Tuesday, May 19 (via Windows Latest). This blog was about the upcoming support for GPU hardware acceleration in the Windows Subsystem for Linux 2 (WSL 2), and the segment that has now been removed (you can still check it out on the web archive) mentioned that Fast Ring Insiders could start receiving builds from the “Iron” development branch (21H1) in June:
Support for DxCore, D3D12, DirectML and NVIDIA CUDA is coming to a Windows Insider Fast build soon. The Fast ring is currently on our Manganese (Mn) OS branch. We expect the Fast ring to switch over to our Iron (Fe) branch toward the later part of June which will expose this new functionality to Insiders.
The edited blog post now says that "Support for DxCore, D3D12, DirectML and NVIDIA CUDA is coming to a Windows Insider Fast build soon once the Fast ring moves back to receiving builds from RS_PRERELEASE." It's possible that the DirectX team announced this June date too early without the approval from the Windows Insider team. Plans can change, but we hope to get more details soon about future Windows 10 updates, including the 20H2 update to be released later this fall.