As someone who tried Roku, Android TV, and Fire TV before switching, better hardware offers a vastly better experience. The Apple TV's hardware is fast. The UI doesn't lag. Things feel smooth as butter. Yes, maybe the Apple TV doesn't need more, but more can be helpful.

In terms of AV1 support, YouTube often only does 4K with AV1 so that's an issue for people.

Personally, I'd love to see an Apple TV that was great for gaming. New Apple processors have hardware ray tracing and decent gaming performance.

I think it's also likely that Apple will try and make an Apple TV that will support next-gen Siri and on-device AI stuff. Yes, you can complain about Apple's AI delays, but Apple's probably looking toward an Apple TV that can support their AI models.

In some ways, "what benefit would a new <insert-thing> have?" Sometimes we don't know until we have it and people start using it.

I wouldn't mind if they enabled the 120 Hz support with the new chipset. I like my TV but the framerate matching feature causes a few seconds of black screen each time I switch between and also drops the UI to 24 FPS. Would be nice if everything just ran at 120 FPS all the time, and since 24/30/60 are perfect frame multiples that's nice to. NTSTC content at 23.976 I'd hope the player would just speed up at that point, but even if not... judder at 120 Hz is better than at 60 Hz.

Also 6 GHz Wi-Fi would be nice. I had to run a cable to my 2 because the 5 GHz airspace where I am is too crowded to stream high quality movies via Infuse without occasional hitching. Same with the seek speed. Meanwhile my iPhone gets 2.9 Gbps of goodput at solid jitter on 6 GHz Wi-Fi.

There's probably some updates to the HDR standards. For me at least though the current one already supports what my TV does.

Also apps seem to assume "because hardware decode isn't available don't serve AV1" sometimes. As silly as that is with the CPU power in the AppleTV, at least that problem would go away with hardware support and they'd stop trying to serve a "compatible" SDR h.264 stream. Despite internet pessimism, sometimes the quality is also raised with more efficient codecs rather than just "the same quality at less bandwidth".

The Bojack example shows that it's not just reduced bandwidth; in some cases you can get higher quality with their AV1 encodes. Additionally if you are thinking of average bitrate, that's ignoring variable bitrates (and the extension, the per-shot encoding params that Netflix utilizes.) That is to say, high complexity scenes get more bitrate than low complexity, so very noisy scenes can look way better using AV1 even while still using lower bitrates, but notably some peaks have similar max bitrates.

The promise of new codecs is reduced bandwidth and higher quality. Probably a new device also has a faster processor and/or more ram in general, which helps with incidental jank. Apple TVs are well regarded and maybe have less jank than other products (I don't have personal experience, I'm interested, but my Apple computer is a IIe so I expect account management issues), but it's nice to get a new Roku every once in a while as bloat/jank seems to creep up on them.

The credible rumors beyond AV1 decode include: Wi-Fi 7 via Apple's home-grown N1 chip, a CPU fast enough to support the next-gen Siri release on-device, a RAM bump, improved pass-through for high-end audio formats, potentially a camera (the new square selfie sensor would be perfect for this) for easier group/family FaceTiming, and more aggressive pricing.