As others have already stated, if account based voting means that all votes are equal, then those with multiple accounts will have the power bias. Currently, accounts can be bought - so we will just see a shift in the way that manipulation of the system takes place (many more accounts).
If the new onboarding system includes a strong form of identity verification then this problem maybe lessened, but it seems impractical to me currently.
I know there are some strong blockchain identity solutions out there. Hopefully Steem can use them to combat the issue. Definitely a work in progress