I saw Williams conduct this at the Bowl back in 2012, and although I was sitting about a million miles away and -- at that point -- had lost both my cell phone and camera (later retrieved), it was still a cool experience. Sorry to hear that he won't be doing it himself this year, but understandable given certain other obligations.
It looks like Williams' plate is very busy until the end of the year--according to several sources he's writing Episode 7 this very moment and then will have to tackle Spielberg's St. James Place (aka "untitled Cold War spy thriller") without taking any break. He will make his annual appearances in Boston and Tanglewood during the summer, though.
I know many Angelenos are sour he won't appear at the Bowl this year, but I guess when you're 83 you have to be very careful about how to spend your best energies.