I am sure this must have been asked many times but please help me understand. what will happen if one billion people were to use Bitcoin as their currency of choice, will the infrastructure be able to handle the traffic and will the transaction speed become extremely slow?
Simple answer, no.
Bitcoin, as it is now can not scale to handle 1 billion people.
In addition, it can not handle 1 billion people making multiple txs per day each.
Because of this limitation, there are proposals and actual projects/tests running now to scale
Bitcoin by using specially designed side systems that use bitcoin as its settlement asset.
You may have heard of them through terms such as: Lightning Network, Side-chains, and such.
Some believe it is possible to scale bitcoin within itself, but there is dispute as to whether this
is safe and fine or will lead to bloat and rapid centralization. This is known to users following
this issue and sometimes (most of the time) heated debate as the "blocksize debate".
The current mindset is to optimize the Bitcoin system and code as much as possible first.