New currencies are being created and they are also getting adopted into the world economy but it is not as frequent as we thought.
The new currencies you mean here, is that the digital currencies?
I am not really sure that we regularly have new currencies if it is related the the currencies used in among countries around the world. What we are using, it is the existing local currencies. Meanwhile for the new digital currencies, I assume not all of them can be adopted.
I heard that some countries have come together to decide to create a new currency that will rival the dollar and from the looks of things they may have a success very soon.
Which countries you refer to? Does it the countries which support the idea of BRICS?
We don't know that it can be a real rival. Let's see first how the idea can be implemented correctly. But if there is a rival of dollar, I think it can be good because it probably reduce the domination of dollars.

For cryptocurrency to achieve this it will be very difficult and I don't think any newer cryptocurrency will be able to overthrown the dollar, the only currency that I think can achieve this is Bitcoin and that is not the purpose of Bitcoin though.
Indeed, it is impossible for a new crypto coin to beat dollar. Even Bitcoin, we aren't so sure that it can be a rival of dollars. Most people only use Bitcoin for the digital asset, its functions isn't as big as dollar.