The whole world doesn't have to become Muslim. This is already a huge problem
NOW.

There are currently 1.5 billion Muslims in the world, and the average life expectancy is 70 years.
A Muslim should really be
of age when they go hajj. There's no point going when you're a baby because you won't remember it. So lets assume that the minimum age to go hajj is 10 years old.
1,500,000,000 divided by 60 =
25,000,000So they need to accommodate
25 million pilgrims every year in order for Muslims to fulfil their compulsary pillar of Islam.

To put this into perspective, that's the equivalent of the ENTIRE population of Saudi Arabia.
Currently, 2 million Muslim go to hajj every year. This figure needs to increase tenfold (and even more in the future!)