When will Flutter for web be ready for production?

Flutter for web is currently a technical preview, indicating that we are still making significant changes. Amongst other issues, the API is not yet stable, performance work is not yet complete and we have known rendering bugs on common browsers. As a result, production readiness will depend greatly on your use case. Our timeframe is not yet predictable because feedback may uncover new issues that we need to work on. Here are a few things we know we need to finish:

Merge into the Flutter SDK.
Make sure widgets are rendered correctly in all important use-cases.
Make sure performance is great for common use cases.
Finish our accessibility work.

Source: https://github.com/flutter/flutter_web/blob/master/docs/faq.md