Nice. Deploying a Scala / Play Framework project on Heroku is painful because the compile times out about half the time. Being able to compile locally and push up a zip is going to make like much nicer.
To be honest I love using Git push to deploy. I just wish it was faster. This doesn't really solve that problem for me - building the slug on my own machine or as part of a CI setup seems like a step back.
That and Heroku's MySQL-compatible service, ClearDB, is very inconsistent, with query times for simple queries ranging from normal to a couple of seconds inexplicably.
[1] https://devcenter.heroku.com/articles/buildpack-api#caching