I think BRICS expansion makes a lot of sense. They are the most relevant country in the respective region. Russia in Eastern Europe. China in East Asia. Iran and Saudi Arabia in Middle East. Nigeria in West Africa. Brazil and Argentina in South America. The idea is to box in West Europe and North America because G7 is entirely concentrated in those region. If G7 are at odds with BRICS member in their local region, they will lose in that region. If G7 cannot influence regions outside their own, they cease to be relevant.The problem with admitting all these small economically countries into BRICS is that the organisation starts to lose it's purpose. What's the criteria for not letting a country in? Can any country that aligns politically or economically with China get to join?
BRICS ought to serve as a counterpart to the G7. When founded, G7 was the largest 7 aligned economies in the world. Things have changed a little since it was founded, but the principle is still there.
It should be limited to $1 trillion+ economies only. South Africa was only really admitted for political reasons, but it would be rude to kick them out. Presently I think only Indonesia and Mexico are the countries that need to be admitted. A seat to the GCC would be a good idea, since they virtually operate as a country.
But the likes of Argentina, Turkey or Nigeria, no. They can join the SCO or the BRI.
In short it is about recruiting various regional power to block G7 influence in the respective region, and therefore making G7 irrelevant.