Is it really the case? Hasn't the industry said all along that the typical gamer is a 35 year old male has that changed? Was that the statistic when *we* were kids? If so then I suspect it will remain the same, these kids will do what we did they will discover the good games when they get older and continue to drive the industry forward and they will buy the consoles for their kids its an endless cycle.
Believe it or not my parents used to be gamers my mom could get the high score on Pac-Man or Asteroids both in the arcades we had and on our Atari, she played NES for a good while too then slowly she stopped gaming as much, Tetris and Mario party from time to time but then Wii came along and she was right there. I saw that a lot people from the 70's who were adults in the 80's, OUR parents, playing Pong, Atari, etc, and they raised US on video games, we grew up and are raising our kids and the cycle continues.
Cell phone games might replace Game Boy (or DS) games and Tablet games might replace PC games in the sense that cell phones will replace dedicated handheld devices and Tablets will replace dedicated PC's, but I even question if that is going to happen. The dedicated game console has no replacement because it serves a purpose. The closest to come along is Steam machine and they dropped the ball on that one.
The gaming market has always supported FOUR different markets, since the early 80's on. It used to be games were made for Arcades, Consoles, Handhelds, and PC's, even when "PC" was divided into about 6 different standards and the industry still managed to survive.
Think of cell phones and tablets as replacing Arcades, the cheap quick pick up and play game you drop a couple quarters in when you are waiting for your food. That is what cell phone games have replaced, the other markets live on unphased. Long term trends still point to a 4 platform market I can see that being sustainable at least for another decade since its lasted 3 so far.