Is it possible that Bitcoin will be regulated? And if it will be, then how would we know 
I have heard stories, speculating that if someone holds 51% of the total amount of BTC they will have kind of a monopoly position and can make or break the coin alltogether. Is this true?
I have heard stories, speculating that if someone holds 51% of the total amount of BTC they will have kind of a monopoly position and can make or break the coin alltogether. Is this true?It is nearly impossible for anyone to "hold" 51% of all bitcoins and if they did it would mean little. It would cost 100s of trillions of dollars to buy 51%.
What you may have been referring to is a 51% attack:
https://en.bitcoin.it/wiki/Weaknesses#Attacker_has_a_lot_of_computing_power
the market cap is currently around 10 billion.. how would it cost hundreds of trilions to buy up 51% of the coins?
Only a small part of the coins is actually being traded. You can't go anywhere near 51% by just buying up all the exchanges and as soon as you start buying on and off exchanges, people will start asking more and more for their coins. Slippage.