Yes, they most likely will be. If you search through the reference assembly interfaces listed here, you should be able to tell whether the functionality you want will be available.
https://github.com/dotnet/standard/tree/master/netstandard/r...
For things like legacy synchronous or Begin/End async methods, we are more or less adding them wholesale to the standard. If something like that is still missing, then it's most likely an accidental omission rather than a conscious removal.
(I work on .NET at Microsoft).