The only bluetooth stylus for iPads that I'm aware of that has an eraser tip is the one made by Paper by 53. It might work ok in a their app but there are software problems getting it to work properly in other apps, such as Procreate. And while it might save wear on the pencil tip the eraser has its own tip that requires replacement.
What I'd like to see in the next gen of pencils is programmable buttons. If one of those could be set to erase that would be ideal for me.