My vision is a RF to WiFi MQTT bridge. I have a number of 433MHz sensors and have written code for Arduino that captures and decodes these into meaningful data. I then send the data to an MQTT broker over the network. This works, but the Uno + Ethernet shield are somewhat bulky and I have to locate the setup near a network connection. My vision is to make it possible to locate such a bridge anywhere that I have power (or potentially anywhere period should battery/solar power suffice). Of course, the RFM chip and the WiFi on the ESP8266 are so much better than the cheapo SuperHeterodyne modules I have been using that I don't know how critical locating the bridge will be. But, I envision having sensors all over the place in the future. I suppose it might be cheaper to just build my own based on ESP8266 rather than use commercial in the long run.
Currently I have Power, Weather, and temperature sensors. I added a WiFi weather sensor recently, but other things are potentially possible.