It's a bad look for both C# and TypeScript. Anybody starting a new code base now would be looking for ways to avoid both and jump right to Go.
If it's the latter, I think the pitch of TS remains the same — it's a better way of writing JS, not the best language for all contexts.
If the TS team is getting a 10x improvement moving from TS to Go, you might imagine you could save about 10x on your server cpu. Or that your backend would be 10x more responsive.
If you have dedicated team for front and back anyhow, is a 10x slow down really worth a shared codebase?