Isnt it hardcoded with 21mio cap?
Of course, but its software. Change the code, convince 51% of the hashpower to use the new code and its done.
I am getting a bit tired of fixing this lie, which is a still a lie no matter how often you repeat it.
Let's get more specific shall we? The proposal is an incompatible change to the coinbase rules. Specifically, instead of cutting the subsidy in half on predefined block numbers the subsidy would be set on a periodic basis by a central authority “hopefully the UN”.
Now you claim that by just getting 51% of the miners to change their coinbase rules you can change Bitcoin. This is not true.
First, the effect on the remaining 49% of the miners and the entire Bitcoin network of somehow convincing 51% of all the miners to produce incompatible blocks would be identical to simply turning off 51% of the miners. Block confirmation times would slightly more than double from about 10 minutes per block to about 20 minutes per block until the next difficulty adjustment time which would be pushed out from about 14 days to about 28 days. So after having to suffer with 20 minute confirmation times for about 28 days the remaining Bitcoin network would be back to normal operation with half the hashing power it had before.
Now let’s look at the miners you somehow convinced to change their coinbase rules. First, they have to find each other and form their own peer to peer network. Oops, without changes to their code all the nodes on the network are going to reject the incompatible blocks produced by all these miners! OK, you can solve this by somehow convincing some/most/half of the nodes to change their coinbase rules to accept the incompatible blocks. Perhaps you promise to pay them for doing it, or, it may be easier to just fire up your own collection of new full nodes all around the world that support the new rules. (One node inside each bank that wants to participate in the new system would do it.) So we end up with one network of nodes and miners that support Bitcoin and a second network of nodes and miners that support the new alt coin.
Now let’s look at it from the user’s perspective. They get to keep their Bitcoins as if nothing happened (well they have the 28 days of slow response time) and they also instantly get an equal number of the new alt coins. Not a bad deal for them.
So, in summary, no,
you cannot change the Bitcoin protocol by simply changing the rules for 51% of the miners and even if you do convince some percentage (any percentage) of miners and nodes to change the rules it only creates a new alt coin that shares the coin history with the Bitcoin blockchain at the time of the hard fork.