Once bitcoin reaches or almost reaches the cap and mining no longer makes sense in a profit sense, I think the volatility will either die down completely or almost completely... After that point, bitcoin will go up or down in linear fashions long term.
That makes sense, but also there is one more important thing which is the volume.
Cryptocurrencies still need to have much more volume than the current volume, so there wont be any significant movement if whales are exchanging their coins/tokens.