Recently Ben posted a picture of a restored TRS 80 Model 100 to his Twitter account. While those machines are completely obsolete, it might be fun to give them some new life by adding WiFi and perhaps some custom software. There are a ton of inexpensive ESP8266 modules out there which let you easily connect to WiFi networks over a simple serial port using AT-like modem commands. These modules are tiny, so they should fit inside a standard Model 100 case.
If there's one problem with this idea, it's that it might be too simple to implement. However, you might be able to make it more interesting with some custom software, such as a simple terminal emulator for the TRS 80, or a menu system that TRS 80 connects to over WiFi.