Is TypeScript ready for serious and productive development?

Yes, we use it in production since end of 2015 and it's great!

The team started as Python programmers and were astonished that the code often worked on the first try instead of producing a series of runtime errors.

At my current gig, we are doing TS development exclusively (frontend) and it's great. Lots of libraries come with types, the community has supplied many more.

With a little elbow grease you can set your backend to generate types for your api requests. This gives you a huge degree of certainty to develop against.

I think so. I worked at a company that was building out a pretty complex system with a front end using React + typescript a few years back, I don't think typescript gave them 1% of the grief that they had with other parts of the system...