Work on this feature has started. Will update here when this becomes generally available.
Thank you for your suggestion and votes.
There are multiple responses to this suggestion.
Support for SQL-like syntax for UPDATE, DELETE and INSERT INTO are not on our road map at this time.
However, the underlying functionality for an UPDATE, SET is essentially a PATCH. This functionality we are actively working on. See this User Voice item here to track for future updates. https://feedback.azure.com/forums/263030-azure-cosmos-db/suggestions/6693091-be-able-to-do-partial-updates-on-document
Thank you for your suggestion.