Heroku already supported PHP via buildpacks,i've been using heroku and php for years,it works very well(a bit expensive though),but I ended up reproducing git deployement on my own servers.
Heroku employee here. Yes there's been a PHP community buildpack for some time. I'm glad you got it working. Moving PHP to be officially sanctioned and "supported" by Heroku is subtle but significant:
We've hired a full time PHP owner. We've got PHP docs on the devcenter https://devcenter.heroku.com/articles/php-support and more importantly the features we document are "supported". If you've got problems with them we will provide application specific support (to the extent of supporting our docs and the platform). It also means that the experience will continue to get better as new features are added, and that PHP has a voice in the future of our platform.
PHP on Heroku has been a highly requested feature, and we're investing a good amount to make the experience a good one.
Product manager for the languages here at Heroku. You could absolutely deploy PHP on Heroku via buildpacks before as you can many other languages such as Go, Bash, etc. This support however makes it much more of a first class citizen working out of the box. Further the richness of this support with Composer for dependencies, HHVM, and proper support channels is fundamentally different than manually finding a buildpack to work for your needs.
The issue i think is managing PHP native extensions deployement.
Even if i require a package through Composer, there is no guarantee i'll have the proper native extension installed(think mongodb ,intl,apc...),w hereas with ruby or node,their respective package managers actually install all packages,including C/C++ ones.
