It should be trivial to do something like this in a Jupyter notebook:
%pip install dclient
from dclient import RemoteDatabase
db = RemoteDatabase("https://simon.datasette.cloud/data", token="...")
db.insert_dataframe(df, table="my_dataframe")
Maybe this API design should imitate sqlite-utils as much as possible - though it will be a small subset of sqlite-utils since the Datasette Write API doesn't handle a lot of stuff that sqlite-utils can do.
It should be trivial to do something like this in a Jupyter notebook:
API design still very much open to ideas.