Thanks for the great piece of software!
Klipfolio is great for vizualization. But preparing data for is it PAIN. Takes unreasonable amount of time.
I would suggest to allow users to use Python to pre-process data. For security reasons you might allow only numpy and pandas modules and run Jupyter notebooks for debugging.
I will be possibly the best dataviz service ever.
Otherwise, if you have other ideas how/where to host the python pre-processing service, let me know. It would be a massive upgrade to Klipfolio.