With at least two EVSE's on the market, WallBox and EVDuty, you can buy an associated current transformer that can be installed to measure the total current being delivered to your home's electrical service entrance. Their current transformer is able to communicate to their EVSE controller to throttle EV charging current to ensure it does not cause the home's service entrance to become overloaded. when the electrical load on the service entrance subsides to some degree, the current transformer senses this and enable the EV charging current to quickly throttle up to take advantage of available headroom within the charging limits that have been set for the EV. In my home I have a 200 amp entrance and most all of the time I have sufficient capacity in my service entrance to fully meet the needs of both my home and an EVSE but there can be rare times in winter when my service entrance could become overloaded were it not for a feature such as I just described. If I had to upgrade my service entrance, where I live it would mean going to 400 amps which would be ugly to look at and cost over $6000. The current transformer accessory available from EVDuty or WallBox can save me from this. I like your EVSE, I like the OpenSource concept, why don't you offer such an accessory so I can buy your EVSE? With EVDuty they can have two of their chargers safely share the the benefit of their current transformer device.
OpenEVSE has been able to do this for years with the solar divert or current shaper feature. A proprietary sensor is not needed. You can use any home automation / energy management system where you can access the data and export to a MQTT server. OpenEVSE can read from the MQTT Server and follow along.
I don't have a home energy management system beyond some thermostats, HRV control, windows and curtains. Your competition offers a $400 Canadian device that measures the service entrance current and communicates by home wifi to the EVSE's from the same device provider. Settings are done from a personal computing device (e.g. a phone) with a browser on the home wifi network. You get status lights on all the devices, diagnostic and status messaging plus documentation to interpret and manage it. No programming is required and I don't know if they use MQTT protocol. Perhaps you can offer VERY specific device(s) to enable the equivalency I have no doubt you can achieve?
Open Energy Monitor EmonPi has everything needed to monitor utility and solar. It has energy monitoring capibility, MQTT server and integrates easily with OpenEVSE.