Say, at some point big banks and hedge funds make an agreement with core developers to remove the limitation of 21M and have the foundation vote for this?
Is it possible in theory and on practice?
The core developers do not have the final say the miners do. If the miners do not accept the new protocol then it will not happen.
I may be mistaken, but would it require the consensus of everyone who uses Bitcoin (as opposed to only those who mine) to enact such a change? I am still fairly new to how the Bitcoin protocol is designed.
Celroc