How likely it would be that a future hard-fork removes this limit or just increases the number of bitcoins in circulation?
This will not happen. It would require the consensus of all the users. Such a consensus would not be possible.
This would destroy the value of bitcoins already mined.
This is why the consensus of the users would not be possible, and why that hard fork will not happen.
Bitcoin has way more branding power than Satoshis.
There is nothing magical or enforced about Bitcoin's branding. It is more recognizable right now because that is the unit that people work with. If people start working with Satoshis (or microbitcoin or millibitcoin, or nanobitcoin), then those will become the recognizable units.
If Bitcoin increases its value, we will reach a point where adoption will be blocked by the general perception that Bitcoin is too expensive.
-sarcasm alert-
Right, just like how adoption of U.S. dollars is blocked by the perception that 1 metric ton of it is too expensive.
-end sarcasm-
People will buy and transact with whatever the appropriate transactional unit is. That unit won't be too expensive, because it will the appropriate size for transacting with.
Also, but correct me if I am wrong, Bitcoins are comparable to shares of a company. The whole Bitcoin network is controlled by the total number of Bitcoins.
You are wrong.
Bitcoins really aren't much like shares of a company at all. They are more like kilograms of gold. The Bitcoin network is controlled by the peer nodes (even if they don't have any bitcoins at all).
If you don't have Bitcoins and need to transact in Bitcoin, you need to buy some and become "shareholder", even if this is for the fraction of time you need to complete the transaction.
In the same way that if you don't have British Pounds and you need to transact in British Pounds, you need to buy some and become a "shareholder" in British Pounds.
Expanding the number of Bitcoins would mean open the network to new users
Cutting the existing bitcoins into smaller pieces would also open the network to new users.
and avoid having a centralized control.
Creating more bitcoins wouldn't do anything to change the decentralized nature of bitcoin.