Hey @markysparks - sorry for the late reply, I’ve been off for a bit.
I could see the value in having a Modbus block where, say you specify a Modbus address and holding register address to read a sensors value
This would be great, and reminded me of some work that @rmorillo24 is doing on a personal project:
Build log: Detecting if the main water pipe breaks - Show and Tell - balenaForums
I also have a small Python Flask web application running that enables an end user to configure the sensor (calibration coefficients etc.) to make things easy when the time comes to replace it. Of course this could easily be done via the Balena dashboard using device variables but that full featured dashboard would be too overwhelming for the people who would be doing this.
This is another thing that we have thought about, and there is some work surrounding. We have been calling it a LocalUI, and the basic premise is to expose configuration and device management features on a UI served by the device itself. Any services on the device could also augment this UI with it’s own UI, such as balenaSound surfacing the controls for volume and multi-room config.
Again, you’re ahead of the curve here, but we have heard the feedback for this need, and we are working towards it. 
@andrewnhem and I would love to get you onto a YouTube stream and chat about your project!
Happy to chat about this if you like…
I will be in touch! 