Yeah... SF mentioned that. You could also simply alter conversion of SP to Rshares for mod downvotes to make them more overcomable. Its really the most easy to address objection. though it bears pointing out that youre taking an already relatively complex system (steemit voting), making it more complex by differentiating moderators and regular voters both of which have seperate sets of voting rights and rewards, then making it even more complex by having the mod - on - mod vote canceling privelages (or the seperate rshare conversion or however you address it)