Great - you bring GPT3 DaVinci to Google Docs. Or Chrome. Or whatever.
You think this hasn't occurred to Google. Or that your prompt engineering is beyond Google? (In reality they're waiting for their own model, or trying to negotiate a large-scale deal as Microsoft did.)
"Extend a popular application of your choice to support GPT3" is likely already on curriculum everywhere for people learning to code.
There's no value-add being one of 1,000 people implementing the most-obvious use case when an API gets released to the world at the exact same time.
And clearly in 2 years time this is wrapped directly by Google & provided by OpenAI directly & also will be a very popular beginner code tutorial project.