Since it is possible to use tokens on the Subject text field of a Workflow Notification, the 128 chars limit is insufficient for most use cases.
The main problem here is the usage of tokens, and if used with token_or, there can be very lengthy subjects.
Just check HTML source code on edit-subject field for a Workflow Notification form.
Increase this limit to, at least 1024 chars.
I know that RFC5322 specifies no more than 998, but for token's sake, this could be even longer than the RFC.
So, I think we can safely increase the Drupal's default of 128 to 1024 on the form configuration.
Active
3.0
User interface