Know that in GENERAL a normal bank lends domestic currency inside of its domestic currency zone. What makes this bank different is that it would lead to Chinese currency being leant outside of China. What follows from that is then you will have more and more entities outside of China who will begin to be in a position where, "They need to find Chinese currency so they can pay back their Chinese currency denominated debts".
Today, much of the world is in that position except they're looking for US dollars to pay off their US dollar debts.
As the amount of Chinese lending to the international community increases, there will be more and more Chinese currency denominated debts, and it will begin to make more and more sense for a nation to hold some of its wealth reserve in the form of Chinese denominated assets. This act will "take away from" the other wealth reserve assets that are used by the international community, and today the front runner for that is by and large the United States bond market (US dollar denominated assets).
So, as more and more nations get behind this Chinese-led bank, what they're saying is that they're on board with the idea that they'll start storing more and more of their wealth reserve in Chinese assets. Simultaneously, because all the Central Bankers of the world can understand that to be more in favor of a new alternative wealth reserve is also to be more against the current wealth reserve vehicles, they're also implying that they think their financial situations are in such a position where they could take a bit of a "hit" to their US dollar denominated assets. This is why as more and more nations go for this arrangement it will become a bigger and bigger deal.
The most natural long run consequence to all of this change would be that the US dollar would end up losing its world reserve currency status. In turn, as more and more nations diversified out of US dollar assets as their primary wealth reserve vehicles the US economy would more and more be forced into paying for its own consumption out of the wealth production of its populace, as opposed to having a good portion of its annual bill picked up by foreigners that comes out of the increased strength of their currency do to all the additional demand it gets for those who are seeking the US dollar as a "wealth reserve for international trade".
The American middle-class is likely to be negatively effected the most from this transition. You see, in America when you aggregate their public and private sector trade deficits/surpluses, you will find that they have run a trade deficit every single year since 1972 (note: they're not lazy, this relates to the nature of the global monetary arrangement that was born out of WWII)... that's 43 years! What that means is year in and year out, without fail, the Americans imported on a NET BASIS more and more wealth from the Rest of the World without there ever being a corresponding flow of wealth coming back to the Rest of the World. This is why America has the massive debt load that it has... when you consume more then you produce, you have to "owe" that difference back to others, and this is why America's bond market is the largest in the world bar none.
So, each and every year currently in America when its done collecting its taxes it finds "it doesn't have enough money" to pay for the services that its government is promising the people. So what it does is it goes out to the world and says, "I need to borrow $x dollars.... who wants to lend me $x dollars? Do I have any bidders at 0.5% interest? Ok... that filled part of my order. What about if I go up to 0.7% interest... anymore takers? Ok good, that filled more of my order. What about at 1% interest? Sweet... the order is full and I've got all the money I needed... thanks". Today, America's interest rates are MUCH lower then the rest of the world's precisely because there is so many foreginers who are participating in those bond auctions because they're choosing to park some of their wealth reserves in US dollar denominated assets. As I'm sure you can appreciate, to the extent that there is LESS foreign demand in those auctions going forward, American will naturally be faced with higher and higher interest rates and will begin to approach more what the rest of the world's governments have had to do for decades which is that their deficits would have to be picked up by primarily DOMESTIC savings.