I cant see any slowness - it takes a 83ms for your example to re-render for me. (although its not a large dataset). happy to debug an example if you can send one with a larger dataset.
also, I was able to render a JupyterChart as it was shown in the altair docs:
import pandas as pd
source = pd.DataFrame({
'a': ['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I'],
'b': [28, 55, 43, 91, 81, 53, 19, 87, 52]
})
chart = alt.Chart(source).mark_bar().encode(
x='a',
y='b'
)
jchart = alt.JupyterChart(chart)
jchart