It is no longer a decentralized currency when a dozen companies control 80% of the network, and we are quickly approaching that point. By the time the halving hits, if efficiency, hash rates, and current MFG. trends continue, you will not be able to break even on your investment with less than a $30k-$100k investment and even then only if you have self sustaining power that has already paid for itself or dirt cheap electric. At that point i can easily see 70%-80% of mining gone commercial and with that, i could no longer support the cause or movement of bitcoin as it would not be a decentralized alternative to fiat any longer.
Bitcoin was never intended to be mined by everyone, that was known right off the bat. There was a great time for home mining, but it is long gone. I would say 99% of bitcoin mining takes place in data centres, probably more. For bitcoin to scale and actually be efficient enough, it has to be through low-cost large scale mining. In a system that handles the transaction sizes of the worlds largest payment systems, everyone mining at home would be a colossal waste of resources, as it would be extremely inefficient and achieve virtually no additional security of the blockchain. If a bunch of bad actors got together and they had 51% of the SHA256 hashing power there would be nothing home miners could do. (Not that I think that will happen.)
Also, I don't think the network has 12 companies controlling 80%.