I had the idea to do the same thing dedicated to Django. I eventually stopped as I realized that I clearly underestimated the amount of work required to make it work better than Heroku.
Totally! The building and deploying is the easy part. Then you have to worry about configuration, secrets, versions, rollbacks, migrations, TLS, logging, load balancing, database hosting, backups, billing, maintenance, reliability, security, capacity, and usability, not to mention marketing and customer support.
The landing page is still visible at https://prodmatic.com