All the features developed in HAProxy, are pushed in the -dev branch of the community version. They are available for free at your own risk (running a -dev code in prod), or you have to wait until -dev become stable. HAProxy Enterprise users might already benefit from this feature in a stable way.

On the opposite, in nginx, some features are developed only in their proprietary solution. Sometime, nginx inc passes for heroes because they open source some of them...