Would be great a low cost Wifi PIR sensor based on (ESP8266) - Reprogrammable.
SONOFF, Sonoff Touch, Sonoff PLUG and Sonoff PIR.
It would be a complete solution.
This could be a modular design with a molex (or phoenix) connector that would allow you to choose the sensor (purchased separately). The app could then handle sending the appropriate firmware to the box based on what sensor you tell it you plugged in.
temp / humid (you've done these already but this would not include a switch)
Hall (ring sensor) to put around cables to monitor entire ring mains or the whole house consumption
this would allow us to set up IFTTT recipes similar to the TH sensors you've already implemented. I know we can do this with the SV Development board but a finished 'sensor pod' would be more elegant, and in-app support would be essential
+1 for PIR sensor. I think is a must for home automation, and also easy to implement it.
I think that you must have more Trigger Devices, to be able to create smart scenes. A PIR sonoff is very important for todays smart home. A PIR sonoff that triggers other sonoff devices and turn them on or off, that is the big deal.