Still cannot use CloudFormation !Sub - why not?

Serverless Framework
1

Why is it still impossible to use AWS’s !Sub function? I currently have to do this:

Id: !Join ["-", ["S3", !Ref StorageBucket]]

which is fine, but seems unnecessary when the !Sub function would be much shorter.

2

Check the plugin:

3

A plugin is nice, but I’m wondering why this isn’t built into the Serverless platform.