I would like to enable OCSP stapling for my app
At the time of writing SSL Endpoints and Heroku SSL (based on AWS Elastic Load Balancers) do not support OCSP Stapling. Whilst there is reported interest from Amazon, there is no firm date for when it will become available.
For any status updates on this we recommend subscribing to the Heroku Changelog if you aren't already. This will let you know about updates, improvements and deprecations ahead of time so that you can make any necessary adjustments.