Just tried the latest development version of the future 4.7 and must say that I'm salivating over the eraser tool.
I'm also a bit disappointed with it too in a way. I mean it works and it's going to be an awesome addition to the arsenal of tools already at my disposal,...but I was disappointed by it's lack of customization options. I mean it doesn't allow me to change the shape of the brush at all and it seems to default to a blocky style when I'm in Calligraphy mode no matter what I do. I hate that!
When you double click the eraser,..there just isn't much there by way of options. I'm hoping that will change as the guys/gals continue to work on it. Other than that,..man it's looking REALLY great and the brush option for the calligraphic pen tool will be what I use ALL of the TIME once I figure a way to make it taper on both ends of the line as opposed to just one.

Inkscape is going to be my tool of choice for my cartooning needs as soon as it's released in 4.7 form. All I care about is the responsiveness and available customization for the brush tool option and the eraser and I'm a happy camper!!!!

I believe the calligraphy tool will have an eraser mode. At the moment you can hold shift to auto-union calligraphy lines as your draw, but there will be a button to toggle this on in future. Likewise there will be a button to do a difference instead of a union which should give you the flexibility you miss from the eraser tool.