There will be plenty of strong assumptions below, since I have a lot of questions and not much time to look for answers.

Given actual adoption, it is guaranteed that exchanges will start powering up Hive and converting Koinos to VHP

We've already discussed potential solution for Hive - financially incentivise custodians to use decline_voting_rights_operation. As for Koinos, one article about some new pool suggested VHP is actually transferable, whitepaper seems to confirm that, which means they are tradeable, which also means that they will be traded on CEXes (I'm pretty sure we'd see bots pushing price of VHP over KOIN at times). Exchanges won't even need to turn KOIN into VHP, because they will have plenty of the latter from their users. And even if they did, if need arises to send out more than they actually have, they could trade VHP for KOIN at a slight loss (or just run traditional "maintenance" to justify withholding withdrawals).

Ability to upgrade without hard-forks.

Seems like EOS at first sight. Which is good, but it is also worth noting that EOS has quite a lot of "native" code for handling time sensitive and/or privileged parts of core contracts, which would need hardfork in case that code needs to be updated. I wonder if Koinos will face the same problem. Also, you still need some form of majority agreement to update core contracts, it is just that nodes don't need to stop and replay using new version of the code, because new code is just a transaction.

Free accounts (bitcoin style)

First of all, bitcoin "accounts" are not actually free. Sure you can pick anything out of its potential address space, but it only gains meaning once it becomes part of state in form of UTxO, that is, after someone sent there some coins. It means someone had to pay transaction fee for the address to emerge from sea of potentiality. Second, we can implement such accounts on Hive (aside regular accounts) - there are very good reasons to have them in context of HBD, mostly for privacy (they would also need to involve transaction fees if not mixed with normal operations - you can either have some privacy for a fee, or you can connect the address to a stake, losing privacy but allowing you to use RC).

People will "delegate" their "stake" to the block producers to mint blocks and earn yield. Spoiler alert: that's DPOS.

There are two key aspects of DPoS. First, it doesn't matter how much support you get as a witness, once you hit top20 you are not getting any more influence on the network (you only mine one block per schedule). This is Hive. In PoS your influence is proportional to the stake you control. Koinos seems to work that way. Second, in Hive users that "pass their stake" to you can change their mind at any time, since they always have full control over their stake. In Koinos it seems like it might be dependent on concrete pool contract, which raises question about practical ability of regular users to verify contract code to make sure they are not subscribing to something that limits their control. Also what ways are there to prevent pool operator from changing the contract later?