Tks @mstormi, here my modest point of view.
Yes, for home application it is a nice solution, I think there are a lot of application it can be used too. For example, if you want to monitor and control no critical system like Brewing Process Control, where you monitor a multitude of variables – temperature, humidity, pH, pressure etc. Those variable are not critical and, in all cases, the process control algorithm must be implemented on a PLC or another kind of Controller. From the SCADA system you only change the setpoint of variables, show the state (not hard real time), show trending chart, manage alarms, configure your system, etc.
Yes, but modbus, for example, is a standard open protocol very common in the industry, but like you say, it’s needed some others binding like profibus, BACnet, DNP3, etc.
This is, from my point of view, the biggest challenge of openHAB as SCADA system.
The “hard” real time control system, normally, must be implemented in the controller device like PLCs, RTU, etc. So you don’t need to care about that, the SCADA system is a human interface and our eyes have a low sample period. All data and control rules will be implemented in dedicated devices. So, If devices send the couple Variable_Value:Time_Stamp it is possible to get the trending chart in any moment.
Neither me, just some very few specific SCADAs in the world have the restriction and certification needed to be used in the nuclear plant. And for sure, this is the smaller market in this field and just the big big companies have access to it.