(I'm not affiliated with this project.)
I like using Markdown for all sorts of "human and machine readable" tasks these days. Text-only formats are really, really nice, and Markdown has formatting-for-display built in, so using it as a text format for defining slides seems like a natural extension to me.
Maybe you're saying, "You shouldn't use slides. You should be writing a memo!" I guess that is a different take from my assumptions which was: "Sometimes I want to make slides. I'd like them to be easy to author and edit in text. Maybe Markdown would be nice..."
If markdown can be used to create your slides, it seems like you're incorrectly using slides as a medium ... when instead, you should be writing a memo.
Note: I'm not hating on the product. Just asking a higher level meta question.