Is it possible with Apple Home Kit and therefor Siri, to communicate with a server with intents rather than communicating with the device, like a light, itself?
I would like to say "Siri turn on the light in Room X", and the light fixture in the room to be controlled by a server, so the intent goes to the cloud rather than the light itself.
You can use Homebridge for that:
Homebridge is a lightweight NodeJS server you can run on your home network that emulates the iOS HomeKit API
It works quite well. I use it, running on a Raspberry Pi, to control (from Siri and also from the "Home" app) a 433Mhz transmitter to control lights and other remote control devices in my home.
There are a lot of plugins that you can install to control devices, but it's also possible to create your own plugins to receive the intents and perform an action based on them.