Thread is not just a software feature, but also requires a specific hardware radio. So by putting it in their hardware now, even though there isn’t a lot of devices using it yet, they are helping you out by future proofing your hardware investment. It’s really a pretty awesome move on their part and I appreciate them thinking ahead like this. Here is their explanation from a blog post last year announcing the gen 2 hardware.

“WiFi can transmit lots of data very quickly, but it’s power-intensive, which is why most connected devices require a large battery or a constant connection to power. To truly be able to add sensors and gadgets throughout your home, you need a reliable connectivity option that requires less power than WiFi. That’s why all new eero hardware comes equipped with a Thread radio.

Thread is the latest generation in a series of low-power wireless protocols like Z-wave, Bluetooth, and Zigbee, but because it uses IPv6 natively, it’s more reliable, and employs secure protocols and encryption by default. We’re the first WiFi system to include an active Thread radio, and believe it will have a big role to play in the connected home of tomorrow. Built right into your eero system, Thread will mean fewer hubs (on your counter or TV stand). And coupled with over-the-air software updates, it means your new eero system comes future-proofed.”

source: https://blog.eero.com/the-second-generation-of-eero/