I think it would be awesome to support ‘slave’ instances which can be anywhere on a network. This would enable, for instance, a bunch of networked raspberry pis each with their own set of sensors to work together without complicated middle layers.
I’m not yet sure if it’d be possible to modify home-assistant with a ‘–slave’ mode, or if this would require separate event loop logic.
It does not really fit the concept of hass. To have sensor arround your house you can install some esp8266 wherever you need. It will be cheaper and use fewer energy.
Home-assistant is not really a sensor by itself but collect data from those sensor.
It is a little bit off-topic but for your special use case regarding the Xiomi plant sensors https://github.com/janwh/miflora-mqtt-daemon might perhaps be more fitting than having to run an additional hass instance on the devices your sensors communicate with, sending the data via MQTT to your homeassistant.