Concerns about commodities backed currency

You know, was just wondering. The BRICS nations are proposing creating their own currency, and it's gonna be commodity backed. But I'm wondering, does it really make sense? Is it really feasible to operate using a commodity backed currency when everybody else is using fiat currency and can play with their exchange rates and can play with their valuation of their currency? I mean, particularly, if you think about a country using fiat currency lending money to a country using commodity backed currency, wouldn't repayment of that loan just mean the depletion of their commodities?

And also when you consider that commodities prices are, dangerously influenced by speculation in the market. So that would mean that the value of any commodities backed currency would be, at the mercy of speculators. So the dollar and the euro, for example, they can play with the valuation of their currency, and then speculators can also play with the value of the commodities backed currency. Meaning that if, say, the IMF or the World Bank or whoever gives a loan to one of the BRICS nations in dollars and then that is converted into, the BRICS currency, when they pay it back, they could end up having to pay back a lot more than what they took. If the value of the commodities backed currency goes down against the dollar, they would have to sell a lot more.

And if it's backed by the commodities, couldn't the IMF or The US or Europe or whoever make a claim on the commodities that are backing the currency? I mean, if that were to happen, wouldn't an IMF loan, for example, just become a vacuum for directly suctioning off the natural resources of a country, or am I not understanding something? It's something to think about.