It will be interesting to see if this is an accurate prediction. If homosexuality is not a genetic fluke, but is influenced by environment, then it is entirely possible for the percentage of practitioners to increase.
Perhaps the number of people who say they are "gay" will remain constant, but the percentage who sometimes have anal sex with another guy will increase.
The data suggests that the number of people experimenting with homosexuality (bisexuals) has exploded 300%... but still is a small number (1.1% among young adults compared to .3% among middle-aged adults.) Either that, or most bisexuals go straight.