We have multiple cases where we need to hide methods in Private.CorLib from IntelliSense:

• Deconstruct method on KeyValuePair<TKey,TValue> and DictionaryEntry - Proposal: Supporting C# 7 deconstruction of certain types. #19397
  • We can work around by shipping the method as Extension method
• Span<T> methods Equals and GetHashCode - Span<T> api update coreclr#8583 (comment)
  • No workaround

There is a risk that we won't be able to move the Attribute to mscorlib on Desktop (similar to fallout from moving ExtensionAttribute down - see https://github.com/dotnet/corefx/issues/13746#issuecomment-265829858)
Desktop options:

1. Deal with the impact of the type being moved in Desktop (compat fallout).
2. Don't attribute the methods on Desktop p i.e. they will be visible to IntelliSense on Desktop.
   • Question for @weshaggard: The attribute matters only for ref. What if the attribute is there in .NET Standard and in Desktop ref, but left out in Desktop implementation? Is that an option?
3. Don't port these methods to Desktop - i.e. they can't be part of .NET Standard.
4. Provide the methods as extension methods on Desktop - i.e. they can't be part of .NET Standard.