I`ve seen this graphic posted on some other forum thread before.
There`s plenty of space for bitcoin to grow,but it`s wrong to compare it to gold.
Gold is used by the people for centuries.All the people without computer knowledge will trust gold,and believe  me,most of the people in the world don`t have a PC,which means that they don`t know anyhting about btc and most likely they will never buy and use bitcoin.