How long is mining actual viable by the masses at the moment? I assume this can't continue to happen unless other altcoins also use GPUs for mining. Won't the d

How long is mining actual viable by the masses at the moment? I assume this can't continue to happen unless other altcoins also use GPUs for mining. Won't the difficulty of mining eventually become unprofitable? I assume this is like bitcoin. However I don't know much about all this.