I have already P1 meter and rfxcom connected to usb.
Then I can share the rpi with you. (later this week,I hope)
I have a Remeha Tzerra and a (buggy) iSense thermostat.
Running beta firmware 4.0a11.hex in the gateway.
I modified my gateway with 4 status LEDs (and a power LED) on the outside, using an 8 display.

P.s. My OTgateway is on the second floor, next to the boiler. My Pi is on ground level, next to the energie meters. I used an UTP connection (3wires) between the OTgateway and the USB connector. That is working fine.
I noticed that I had to connect the USB to the raspberry and then restart the OTgateway.