Definitely something to this. The only negative I can think of is that it would be controlled by a person (or group of people). This would always leave some wondering if the account owner wouldn't just start (e.g.) upvoting their own posts once the account got large enough. This is in contrast to a smart contract, where theoretically anyone can verify the code/behavior for all time.
It would seem like you'd have to have some governance structure. 5-of-7. 2-of-3. etc. Or perhaps what you've stumbled on is an enDAOment? It would grow on it's own through capturing inflation and a governing board could decide how to direct it. Maybe a governance token to allow voting might be interesting.
At the end of the day though, you're still trusting people to implement the results of the vote, and with this approach, HP can only go in and never back out. So people have no recourse if the account starts being used for nefarious purposes.
Not trying to be negative, just working out potential issues. One question would be: why would I powerup HIVE to this account? I can support projects I like using my own HP/upvotes. I think the answer has to be that the owners of the account do the leg work of finding good projects. I don't want to have to follow/research everything myself but do want to support the ecosystem. But that's what delegating is for, right? Why would I power up HP to this account instead of just delegating HP to it? After all, that lets me get my HP back if the account ever starts doing things I disagree with.
Yeah I'm starting to lean more on a multi-key system instead where 3/5 or 4/6 highly reputable members have to sign messages to make changes with the keys to lock either leaked keys out or mismanagement.