Would love to have a renderer that outlines/highlights waterlogged blocks, as it would be useful to see (in my case anyway) leaves that have been waterlogged even when graphics are set to fast and transparency isn't available.

Thanks,
pointy

Can't you do that via a resource pack and adding some custom texture for waterlogged leaves? That would be the best way to do it performance-wise. Anything MiniHUD renders as extra will always have an impact on performance, both when updating/generating the overlay and when drawing it every frame.