BRICS can add as many members as it wants, but will it be able to sustain itself forever? I doubt it. I believe the bloc will get smaller in the long run, as most member states (countries) will abandon it due to poor economic performance. Only China and Russia will survive due to their economic strength. At least, that's what I think will happen in the future. But rising "de-dollarization" efforts could change the game. Only if they prove to be a success.
The fact that more countries are joining BRICS and even more are showing interest to join, shows that there are a lot of benefits in dedollarisation and the multipolar world and they all see it. In the future, the members can definitely change. Some may go away, some can be kicked out as dead weight, some new members can join but everything will be constantly changing until the World Order is finally established. That's the nature of transitional phase. In fact this is one of the reasons why BRICS is moving ahead not as fast as we hope.