I’ve worked with Blazor for about a year. It can be extremely productive for writing real internal business applications. “Backend” people can easily make interactive user interfaces and utilize their C# skills.
I think the threat to Blazor is that productivity in general in organizations is not enough prioritized in comparison to dogmas or current trends. For example that now a days you “should” have a separate front end team and that front end team “loves” technology X (for example React).
That's my experience too, it's near perfect for internal tools like admin panels, where you don't necessarily need to hire dedicated front-end engineers. UI might be a bit ugly, but that's okay for internal use. Usually, admin panels end up having a weird assortment of buttons the real frontend doesn't even need, so creating REST API dedicated for that, and then React frontend to go with it is not time well spent.
This also depends on your backend engineers or whoever ends up maintaining the internal tools, are they comfortable using Blazor or not?
If you need frontend engineers and designers then going with React and the mainstream is wiser.
Although it is not that difficult for a front end dev to spend a week of time or so to create a custom styled component library in Blazor for your company and get things looking good and branded by default.
I think the threat to Blazor is that productivity in general in organizations is not enough prioritized in comparison to dogmas or current trends. For example that now a days you “should” have a separate front end team and that front end team “loves” technology X (for example React).