The most interesting problem they are trying to solve is the way this integrates with their addon partners. Typical CI you specify services like MongoDB, Redis, Postgres, etc. to be installed directly on the image that your tests are running. Heroku seems to be literally creating accounts with their partners, forcing them to spin up necessary resources, and then just churning the account as soon as the tests are done. Most Heroku partners offer a free tier assuming they can get a percentage to switch to the higher tiers, but this is going to increase usage of those free tiers by a very large amount and I don't see it converting well for the partner.

Edit (clarity): They didn't solve the problem yet, and are limiting the addons to just Heroku services (Postgres/Redis) until they figure out best way to handle with partners. I will be keeping a close eye, very curious what they land on.