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?
I think 51% miners need to accept 21M+ coins to have those mined coin's transactions be included in new blocks. If >50% miners agree ...this can happen but that would actually be the fall of their own wealth, coz services running on bitcoin will immediately shift to some alt.
p.s. Bitcoin is not only protected by code, but also by market economics 
I think big players could easily control 90% or more of all hashing power. Say, a megapool driven by asics on hundreds of acres at Greenland or Alaska.
Disclaimer: I am not going to spread FUD, just want to share some thoughts and find answers