Our current application is now running on ASP.NET Core (MVC) and I was wondering is there will be an offical way to use MVC and Blazor (client side) in the same project?
This is definitely now possible for server-side Blazor, Chris Sainty's blog (and the source for the example in that blog) gives an example of exactly how to do that.
Personally I prefer to have the Blazor components in a separate project in the same solution as the MVC project. There are a few reasons for that:
I tend to do the initial debugging with the Blazor project set as the startup project and then switch to the MVC project when I'm ready to integrate the component into an MVC page.
If you want to try that approach, my answer to the question Adding Server-Side Blazor to an existing MVC Core app gives a complete walk through of how to add a separate Blazor project to an existing solution that contains an MVC project, and then how to use those Blazor components in the MVC project.
I expect very similar approaches would apply for client-side Blazor too, but I haven't tried that yet.