I also think South Africa would look favourably on the Cuban application, given Cuba's role in supporting the struggle against apartheid.

Cuba is a rich nation when its borders are open. And with all the sanctions flying around from the US, I can see a point at which you can do business between Brazil, South Africa, Iran, Russia, and China without ever touching an American market, simply because so much shit has been added to the sanctions list.

Currently, a country declares itself interested in joining BRICS at which point there's a process of consultation between the chair of BRICS (who talks to the interested party), the foreign ministers of BRICS (who talk to their own leaders) and then the heads of government themselves. With the latter you need to build a consensus towards extending an invitation. Once that happens the country joins as soon as its leader chooses to. It's also not like the original 5 are BRICS' security council. The consensus includes all 10 members.

Ironically, had Milei let Argentina join he could play a spoiler and deny Cuba entry.