It would be awesome if Scapple would support [this](brettterpstra.com/2013/08/18/mar … -mind-map/) or import markdown lists directly.
I’m not sure how that would work, since Scapple isn’t a mind-mapping program in the sense that these are. Most of the programs listed automatically arrange things in a radial forking pattern based on a strict hierarchy where every object has at least one up or downlink, and most have two. These things have more in common with Scrivener, really.
As for lists, try dropping your .md file in, and specify
<CR>* as the separator. It will work for very simple single-level lists.