HMD lets humans interface with the world of the computer. Reality capture lets the computer interface with the world of humans.
Reality capture feeds smart contracts; if the AR cameras see you're low on some stock, "the computer" can order more, and direct the people to pick them up. Smart contracts are a reasonable mechanism for doing that.
Block chain is a shared ledger that's suitable for multiple entities tracking anything (say, reality) together, and a communications medium that's good for things that need to be auditable (say, tasks).
The associated complexities and limitations with blockchain ledgers are a lot. The nodes must be propped up by large amounts of computing power, which only big companies/groups can provide, not individuals. And it's not as if the government can't be trusted, there are so many stock market indices & financial markets that aren't under anybody's control.
BC does this by letting everyone submit answers, but making it really hard (computationally intensive, aka, burn electricity) for your answer to the be the one that's accepted.
PeerCoin (to pick one) does this by making your likelihood of being The One correlate with your investment in the worth of the coin (literally how many of the coins you control). If you're the One, either your answer is accepted, or you're selected to give the answer, and then it's accepted - I'm not sure which.
You can also limit participation in your blockchain in combination with these; for example, a closed (invite-only) bitcoin would still burn electricity, but not nearly as much.
