It's so unwise to add an artboard to a simple sparkle looping animation. This is necessary when creating a component that repeats two or more states over time in a single component (eg cursor blinking).
The "Import Videos & Animated GIFs" feature is marked as "Feature Started" on uservoice, and it should do that for us. I imagine it's the reason they don't bother improving the available tools to accomodate single artboard animations in Xd.
In that context, a simple timeline functionality would be best, but we can only wait for now...
Hopefully we get it sooner rather than later, since it's been the most requested feature and it's essential as everything uses animations and video these days.