Let's say that, hypothetically speaking, someone had the mining power to mine all unmined bitcoin(I believe around 6 million bitcoin, correct me if I'm incorrect). Would they confiscate it off of them? Would there be some kind of software barrier? which would mean that even if you had such great mining power, you wouldn't be able to mine so many bitcoins.
Then all those bitcoins would belong to that person. There's nothing in the current Bitcoin protocol that prevents this.
I don't know what you mean by "would 'they' confiscate it". From the point of view of the Bitcoin protocol, nobody has the authority to confiscate bitcoins.
Of course, if this happened, it would mean that miner would be able to unilaterally decide which transactions would be confirmed, and they could also reverse past transactions by re-mining part of the chain. They would be able to allow people to double-spend. This might well cause other people to lose interest in using Bitcoin, since its security would be undermined, and this could cause the currency's value to fall, perhaps to zero.
The problem with all of these "what if X amazing ability is discovered by someone" (SHA-2 breaking algorithm, near infinite computational power, etc.) is that a person/government with such an ability would be better off keeping the ability a secret to sell or use than using it to publicly destroy bitcoin (which is what this would do)