In addition to the currently allowed syntax (stackalloc int[3]) we should allow stack allocated arrays be created with initialization:

stackalloc int[3] { 1, 2, 3 }
stackalloc int[] { 1, 2, 3 }
stackalloc[] { 1, 2, 3 }

• Proposal added (https://github.com/dotnet/csharplang/blob/master/proposals/csharp-7.3/stackalloc-array-initializers.md)
• Discussed in LDM
• Decision in LDM
• Finalized (done, rejected, inactive)
• Spec'ed

Discussed in LDM in Jan 2018 (link to meeting notes TBD)
Prototype dotnet/roslyn#24249