You state several things that I completely disagree with...Of course this is all subjective, so I certainly won't say you are wrong. But here are my thoughts relative to yours:
You:I suspect there won't be an ATV 5.
Me: I think there will be, albeit not for at least 1 year, likely more like 2 years.
You: The 4 is a dud with very little developer interest and it was technologically basic back when it came out a year ago, let alone now.
Me: I've used a wide variety of the current streaming boxes and a handful of SmartTVs. I have not used the Nvidia Shield. Compared to the others, I feel the ATV4 is superior for my uses. And that is a very big key: for my uses. I couldn't care less about games or a huge library of apps. However those I do use, in particular Plex, run exceedingly well on the ATV4 and in my experience as good as or better on the ATV4 than on other streaming boxes.
You: It's next to impossible now to buy a TV which doesn't come loaded with Netflix, Amazon and the rest, so a stand alone box which doesn't even have Amazon Prime is a very hard sell.
Me: I have used SmartTVs, and have been completely underwhelmed by every single one I've used. I am sure there are some out there that would be better, but those I used were horrendous (and that does include mid to high level Samsung sets, so I am not referring only to low end models). Further, the ongoing support and software updates of the multitude of SmartTVs certainly will not keep pace with dedicated streaming boxes.
You: Roku will hang in there for a while, but their days are numbered too
Me: The market for streaming boxes is absolutely mammoth. This is not a 1 per household device, many houses have multiple TVs and will thus eventually have multiple streaming devices. This space is in its infancy.
Ultimately, my feeling on streaming boxes is that none are perfect, and that none will likely satisfy every want (notably Amazon Prime not native on the ATV4, AirPlay not on Roku/Fire, etc.). But much like people have had multiple inputs to their TVs in the past with a cable box, bluray player, game console, etc., they can just as easily have multiple streaming devices on a single TV. Pick the device (or devices) that work best for your viewing needs. But to say Roku's days are numbered, that there won't be an ATV5, and other doom-and-gloom about this space is way off base in my opinion.
