I haven't been letting my downvote power sit idle here on Hive, and I've found it much easier to help deal with haejin, a straightforward single account self voter, placing votes high on the curve; than crystalliu, a network of accounts shuffling stake, creating dozens of spam posts and voting at much lower curation curve ROI. Anecdotal evidence, sure. But in both cases vigilant community efforts and the use of downvoting are the only remedy. A code change would be only a minor impediment.
If anything, I would advocate for the removal of self upvotes to occur entirely on the User Interface level. I imagine with Hivemind it would be possible to simply not show a like button when condenser or the PeakD UI sees that the post is created by the logged in account. Any user who is going to set themselves up on an outside auto voting bot or some other solution is already savvy enough to get around a blockchain level restriction. Removing the option from front ends would at least set the social expectation for new users and general public that self voting is frowned on and not a community standard.