Yes - OGEMA is the goal but sounds a bit too big at the moment. So the intention is to develop a prototype of open source EMS which can control devices (heat pump, AC/DC-converters with 0-5V input or RS485 ModbusRTU, swiches …). On the input side we need values from powermeters like e UEM-80 or EM300 (with existing openhab-bindung).
The problem is that devices are not at the same place. If every device would get an own RPi I think thats overkill (people in pv-forum suggested this).
So the Arduinos as “extended arm” of the controlling RPi looks more perfect. The main advantage would be only no or less updates of firmata and only 1 RPi-system with (maintained) Linux.