1. Apple TV 3 had a single-core variant of the A5. Most A5 chips were dual-core. Could the Apple TV 4K have a triple-core variant of A10X?
2. Getting 3 GB is probably necessary given it's more advanced requirements, but it's going to sting a little bit for the iPhone 8 buyers who will likely be stuck in 2015 with 2 GB RAM. This is especially true since the iPhone 8 will likely cost 3X-5X as much as Apple TV.
3. The reason for dual HDMI outputs is NOT for image quality, because the image quality will be exactly the same unless you have a receiver that is intentionally changing the signal. The reason for dual HDMI outputs is for HDCP compatibility reasons and for audio track support. For example, my 4K PVR will not work at all with my 1080p TV through my 4K receiver. I just get an error message saying HDCP 2.2 is not supported. However it works just fine connected directly to my 1080p TV, because it knows to correctly downsample to 1080p and forget about HDCP 2.2 in the latter scenario. Unfortunately, in this latter scenario any advanced audio tracks will not work because the HDMI is going directly to the TV, and bypassing the receiver. Having a second HDMI output would allow advanced audio tracks to be decoded by the receiver. This also helps in the reverse scenario where you have a 4K TV, but an older receiver. These older receivers often cannot transmit a 4K signal, so anything going through it would be limited to 1080p. With a dual-HDMI player, the 4K TV gets 4K and HDR, and the older receiver can decode TrueHD tracks, etc. since each component would get its own HDMI connection.
4. A 25 Mbps connection is sufficient to stream 15 Mbps, according to Netflix, and it's probably true in most instances unless your internet service provider is unreliable. However, even if 25 isn't quite enough with crappy ISPs, 50 Mbps is commonplace in urban areas. I have 1000 Mbps, but the norm in the area is 25-30 if you're cheap, and 50-60 if you're a bit less cheap. Mid-range cost is 100-150 Mbps, and higher end cost is 300+ Mbps. I pay CAD$76 per month for 1000 Mbps, which works out to about US$63 per month. So, the main concern isn't speed IMO. It's data usage. I have unlimited data usage, but many people don't. I only use about 200 GB per month, but many high speed plans up here are less than that, while many people will use significantly more than 200 GB per month.
5. 4K isn't just about 4K. It's also about HDR. HDR is great. Unfortunately, my main movie device is a 1080p projector. To get true 4K HDR means about US$8000, or fake HDR with 4K is about US$3000-$5000 in a projector. I went with the 1080p Sony VPL-HW45ES which at the time was around US$1800, and will go 4K later. Nonetheless, if the Apple TV 4K is decently priced, I'll buy one. I've been meaning to get another Apple TV, and I may as well get a 4K one. It turns out that most streaming 1080p is worse than 1080p Blu-ray, but streaming 4K is better than streaming 1080p. It's also true that streaming 4K downsampled to 1080p is can often be better than directly streamed 1080p. Unfortunately, most machines just stream the 1080p stream if it detects you aren't using 4K.
