I got your point, very constructive. Here is my thought:
1. Bridge between the RF module and the internet
If all the processing is done on the host pc side, leave the device only having the sensor to detect the state and
being driven by the host pc, then it will be a lot easier to build the device itself, don't need that much functionalities. This should be the direction.
2. Transmission mechanism should not be a problem except the worrying about the wifi cost since it has all the necessary functionality built in with encode/decode, security and compression/decompression which becomes a heavy burden on the device side. But it should be easy to resolve by embedding a Linux kernel with the wifi stack.
3. SDR might be a solution to deal with various RF protocols, but do you think the performance will be compromised than using the hardware components?
So all of the available or to be defined protocols and mechanisms can be tested out if the platform supports simple/thin devices. Your proposed embedding wifi module is a very good solution to meet this requirement. Do these products have FPGA or SoC with UART or SPI interface?
If you are interested in further discussion, maybe we can take it offline. Shoot me an email at danmark.clara _at_ yahoo dot com.