Although we still serve less than 4K resolution (we've not found demand yet), I can confirm that NONE of the things said in the article like TV set age or contracted internet speed are in the top list of issues that we are dealing with on a daily basis.
In our experience, what is giving us most of the headaches is the network congestion at the time of download/stream; at weekend nights some ISPs just can't deal with the amount of traffic that this kind of services are demanding. We are spending quite a lot of resources in customer service for this reason. Unfortunately, at the end the solution is always the same, "please, try again later". Of course, this is not something people like, specially when they have paid for the contents they intend to watch "now".
Surprisingly, people who have contracted a low speed internet connection seem to be already aware of his connectivity limitations and are not much of a problem. However, the ones who have good connections are not aware of the peering agreements his provider might or might not have with other networks[2]. Some might be even suffering from bandwidth throttling without even knowing.
[2] We use AWS Cloudfront CDN. We've talked with other netflix-like services, and although they use other CDNs, they still suffer from the same problems like us.