As someone already mentioned, I can't say for equities as i've never traded them, but futures are still plugging along. Yeah it's a lot slower and more range bound, but reading the order flow is still fine.
I don't think day trading is dead (hope not anyway) I just think the markets are in the transition phase where it's a case of adapting to the new world or move on...
I think that link, as someone else already mentioned, mis quoted the prop firm letter a bit to fit his opinion. In the letter he stated that they were letting the less talented traders go as the days of someone being able to grind a 50k a year living is over. Now in my opinion, if someone is only just able to grind out 50k USD a year and needs big volatility and volume to do it, then they were never really gonna last long anyway.
Personally I just see this as a big flush out of the day traders who don't really understand how the markets work. For example, 95% of the market are trying to find trends, using various trading systems, and the conditions as of late would of wiped them out. I also think the big volatility for like 2008/2009 gave less talented traders more room for error. They could take 4-5 losses in a row, and have 1 good trade that would put them in profit. Now you have to be razor sharp.
I think if you're able to adapt to conditions yourself and have a fundamental strategy that you can adapt between the conditions, then you'll be fine. If you had a one size fits all strategy, then either adapt or move on.
Personally i've quite enjoyed it recently, and if ES stays like this, it wouldn't bother me.
Trading will go on.... The day it ends is the day the world ends.