You can’t simulate the physical remote, they are very nice remotes besides the service itself.
To my knowledge the only thing that would kind of work like Harmony (but with quite a bit of elbow grease) would be a Flirc sensor and an IR remote of one’s choice, but that’s still IR-only, no control of Bluetooth things like an Apple TV or a PlayStation.
It’s a real shame they’re giving up, because things like HDMI-CEC are laughably useless for any scenario in which there’s an AV receiver between the media device and the TV.