Current plan is to use list-based feed of the Google Data API[1].
There are three known issues:
performance - to delete/update 100 rows Teiid must generate 100 http requests
consistency - user wants to update 50 rows. After the 10th row is updated the connection could fail which would cause that 10 rows would be updated and 40 wouldn't.
headers - update, delete and and insert statements will be supported only for the spreadsheets that have a header for each column (headers are in the first row of a spreadsheet)

Select statement is implemented using Google Visualisation API, but this API doesn't support updates and doesn't return row numbers.

[1] https://developers.google.com/google-apps/spreadsheets/