Today, the Heroku Postgres team released into beta the new basic plan, $9 / month version of the free dev plan.
Accompanying this announcement is the implementation of a 10,000 row limit on the dev plan. This row limit was designed to correspond to the 5mb limit on the existing free shared plan.
Please note that these plans are still beta, and Heroku Postgres has not yet announced a migration schedule from the shared plan. However you can start using these plans today.
Read more about the new plan, and the mechanics of the row limits on the Heroku Postgres Blog.