Describe the feature

It would be very useful to a block like this (also the not "slab" half only):

It's two existing blocks placed back to back

and a version of one that's two of the above with one rotated 90º, like to fit in a situation like this:

The combination of a Slab Edge and a Slope Edge makes sense to me as well as the corner variant, though I'm not sure what you mean with "the not 'slab' half only", do you mind elaborating on that?