I’ve ridden primarily “enduro” type riding and DH up until this year. Although I haven’t yet done the strength program above I have looked ahead at it and it will definitely help in enduro riding. If you are racing or plan to race I think a lot races are won and lost in the corners, the strength work and intervals are really going to let you put the power down coming out of corners where others will potentially struggle. You also really need to spend a lot of time on the trail riding very technical DH (not flow trails) to help build what James Wilson calls “high tension cardio”. There is nothing like trying to navigate a nasty down hill section with your heart rate in the 180bpm range while you are trying to pilot the bike and keep off the brakes.
I would say you are going to need to add in upper body work and grip strength for sure. You also really need to nail and stay on top of your core work. You need upper body strength to keep yourself from smashing down into the bars on big hits and grip strength to fight off the arm pump during long descents. In almost any youtube video of DH or enduro riding you see riders collapsing after big hits - this is from a weak core and upper body after blowing through 5-7 inches of travel. I would add in pull ups, push ups, deadlifts and farmers carry if you can handle that much volume. I would be careful though, last year I followed a 6 months strength enduro program along with structures interval training and I was cooked in February. I learned a lot but 3 days in the gym plus 3 days of intervals was to much for me to handle at the time. I think my nutrition planned a big role in that too.