You're correct on that Jonas for now- we're also playing with an in-app player concept as well which would pull from InVision down the road. Regardless the goal being to have it be a hosted artifact you can easily share for feedback (something we didn't have in beta version).
Looks great! Have I understood it correctly - in order to test the prototype, I have to upload it to Invision first? I can't preview it in Sketch?