It cannot keep increasing forever. The higher the value, the slower the increase. I'm certain that if we reach $500k then that's the time that it will take months or years to see it increase again.
The only thing that bitcoin's value will keep increasing is the supply and demand. It should go up as long as it is useful. That is why we should inform, educate people not only for the value of bitcoin but to what really bitcoin can do to us. Bitcoin will grow more as long as it is useful.
Yes it won't increase forever and all we need to do is share our knowledge about bitcoin.