I was just thinking... the wemos probably has enough pins spare to attach a temperature sensor... I wonder how hard it would be to add a screen to the clock so that it cycles through TIME > DATE > TEMP.
Disclaimer: I only have the schematic for the IV-6 Wemos clock kit. I believe the Nixie and DA-2000 versions of the kit are similar (but not identical for obvious reasons).
The schematic shows D0 as unused and if you were willing to give up the button or the PIR then D3 and D4 would be available too. If you use a DHT-21 for your sensor you only need 1 GPIO. Libraries exist for interfacing the DHT family of sensors to the ESP8266.
So it looks like it is feasible. The rest is up to you. If you are a reasonably capable Arduino / C++ programmer it won't be difficult. First you need to ask Ian for a copy of the source code (technically this clock isn't open source). Then get to know how the program works, Then add code to do what you want it to do. Talking to the sensor should be easy. Modifying the display logic to display the temperature and humidity will be a bit trickier.
Look into it later when the dust is clearing off the crater.
Unusually, this board doesn't have an exposed I2C header on it - the size of the board just didn't allow for it. Normally I would say that would be your first stop. If you wanted to go that way, you could pick up the SDA/SCL fairly easily from the header on the Wemos.
However, if you are not using a PIR, probably that will be the way to go for the DHT21.