In some ways I agree with you, however in other ways the open letter does come across as sounding quite entitled.
I do agree I think the homebrew scene for consoles peaked with the original Xbox, however tech wise that was a different world to what we live in today.
At the time PC's we're very expensive, a lot of people we're only just getting computers. If you had multiple in your house you'd be doing pretty well for yourself, even broadband was a luxury in the early 2000's.
An Xbox which although was quite expensive (in my opinion been a teenager in School back then) was a lot more affordable than a computer. It could easily connect to TV's and HDTV's and was networkable, so the potential to do things we take for granted today when hacked was massive.
Keep in mind back then for a DVD player that would play Divx and Xvid you would be paying £500+, yet you could hack an Xbox Classic which was significantly cheaper and do so much more with it.
With that in mind their was a lot more interest in hacking it and security was not that great back then.
These days you can get a £30 Raspberry Pi which can do most things people want from a hacked games console, people are walking about with phones which are now more powerful than the last generation of consoles are and are capable of emulating the Wii and GameCube.
I personally do love the homebrew scene on consoles and messing about with my stuff making it do more than intended, sadly it's just not that beneficial these days.
The PS4 does have pretty good ports of Linux where its processing power can be used, e.g. video encoding. Heck i've even run Dolphin and Steam on my PS4. Fail0verflow have contributed a lot to the PS4 kernel / driver wise. All that really needs to be done in improved GPU / Audio drivers.
I do get the feeling the vast majority just want piracy and cheating though, which is why i think if people want to willy wave on social media then let them. They don't owe anyone a thing and likely know it will be mainly used for piracy. For them the challenge is breaking a secure system, if you can do that then fair play you earn bragging rights as it takes a lot of talent to do that.
I would like to see a PS4 Homebrew scene, if it happens i don't think it will be anything like consoles from previous generations though.