I assume that the 21 million bitcoin limit can be changed if there is an agreement to change the Bitcoin specification.
It could be changed if the majority of all users agree to use a new client with a changed Bitcoin protocol.
If miners earned the same amount of bitcoins over time, then there would be no upper limit for how many bitcoins can be mined. That would perhaps make the price of bitcoin more stable and make bitcoin more suitable as a general currency.
Right... how the hell would an unlimited supply of bitcoins result in a more stable price than a predictable, limited, already known fixed supply of bitcoins?
And how the hell would it make Bitcoin more suitable as a general currency? The supply of bitcoins is by NO means a problem whatsoever to act as a general currency.
Suppose that instead of 21 million, there would be a total supply of 314159265 trillion bitcoins. Would that be better?