I agree some more talk about motivation would be good. I know it's supposed to be a simple introduction but since you start with shape types, you could talk about the [Circle-Ellipse Problem](https://en.m.wikipedia.org/wiki/Circle%E2%80%93ellipse_problem) which for me highlights pretty clearly the issues with inheritance. Variants solve that by allowing one to change a circleKind to an ellipseKind.
The big thing variants let you do is have a seq of different types seq[Enemy] etc. I agree types should be nouns not verbs. A line needs two points (4 numbers), and a circle needs at least a centre (2 numbers) and a radius.
