For HVIF icons maybe there would be a way to override the stroke outline color either in the icon data or while rendering, which could improve how the icons look on dark themes. Though I don’t know if there is any consistency in the name of that style in the various icons. Though that could may be fixed with a bunch of icon updates.
That still doesn’t solve the problem of completely replacing an icon though. But that can probably be done in a reasonable way given this is Haiku and not Linux.