To me, it seems that one could read an (unsaid) implication in your original comment that is “and those advanced features will only ever be behind a paywall” — as I think in nginx’s case that’s actually true for some features (but I might be remembering incorrectly!), and by listing and comparing HAproxy and nginx in that manner I can see that implication. But that’s being kinda nit
picky, though if I was an HAproxy dev and all features were developed in the open and released into the mainline for free in a new stable version in the future, I would probably read it that way and be a little miffed, I suppose
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...