Microsoft did - in both Azure AD [1] and Bing [2],[3]. 1 and 2 from .NET Framework to .NET Core, but [3] is to .NET 5.

[1] https://devblogs.microsoft.com/dotnet/azure-active-directory... [2] https://devblogs.microsoft.com/dotnet/bing-com-runs-on-net-c... [3] https://devblogs.microsoft.com/dotnet/migration-of-bings-wor...

Saw impressive performance jumps on a full Core 3.0 -> Net 5 upgrade in 2020.. looking forward to testing out 6 (post preview).