It seems very unlikely. There's basically zero benefit to multigig ethernet on an Apple TV. Even if you're streaming the highest-bitrate 4K Blu Ray source material you can get your hands on, we're talking about something in the 100mbit range (45GB/hour). Gigabit ethernet has ample headroom for media playback, and it's essentially impossible to saturate outside of getting faster downloads - and how often are you actually downloading something on an ATV?
The only scenario where I could see this happen is if Apple were to include a couple TB of storage on the device and have it be a combo ATV + Time Capsule. An always-connected network device just passively storing backups of your network's Apple Devices, while also serving as a media center device, would be a dream - but I'm not sure there would be a decent enough market for what this would cost vs. a Mac Mini.