I'm really excited about this work, although I haven't read the code or paper yet. It seems to me Fractal would be ideal for running benchmarks for compilers so that the OS-induced noise is kept to a minimum.
An alternative to Scrappy is the free CodeBoot web app (https://codeboot.org), which allows you to create web apps in Python that are fully encapsulated in a URL. No installation is required—neither for the developer nor the user. Below is an example of a math practice app with simple user interaction through dialogs. To create a web app URL, right-click the "play" button and choose the type of link you want to generate.
For more complex UIs, CodeBoot provides an FFI for accessing the DOM directly from Python code. For example here is a dice throwing app with a button to roll the dice again. The text in the button has translations to multiple languages and will adjust to the browser's default.
Author: do you see issues with that use case?