You were already using F#'s syntax for C# NuGet references in .NET Interactive. Even NuGet itself labels this syntax "Script & Interactive" in its picker.
https://github.com/dotnet/interactive/blob/main/docs/nuget-o...
Now you've created a new dialect.
.NET interactive uses a dialect of C# - the script dialect. With file based apps, we strive to use the standard C#, so you can convert file based apps to full projects at any time.
That doesn't explain why standard C# had to deviate further from the script dialect just for import directives. These directives don't interfere with the rest of the grammar.
Is #:package <pkg> really so much nicer than #r "nuget: <pkg>" as to deserve deviating from .NET Interactive, F# and the existing NuGet picker? (It could be, if properly argued!) Has there been any effort to have the rest of .NET adopt this new syntax or share concerns?
On that note, is any language other than C# supported for `dotnet run`? Is the machinery at least documented for other MSBuild SDKs to use? Considering how dotnet watch keeps breaking for F#, I suspect not.