Part of the 0.4 release is to incorporate the concept of abstract rendering - which means you render on the server, and then send the necessary information over to the client on demand. For example, if someone tries to scatter a billion points, instead of just drawing a useless point cloud, you would figure out where all the points fit inside your 512x512 canvas (or whatever size you have), figure out how all the points stack up, compute an alpha that is meaningful for that number of points, and then send the heatmap to the client.

You can easily imagine as similar approach for line plots which does selectively downsampling of datapoints in order to preserve interesting features in the plot.

And then we'll build interactors on top of that, so you can actually treat it like a scatter plot, even though it's a heatmap that's being sent to your browser.

So the answer is - large datasets, means, as large as our abstract rendering algorithm can handle on your hardware, so those data sets should be pretty big.