Yeah .NET Core 3.0 will address some of that, not all. I suppose for any brownfield development looking at switching across those things are the potential blockers at the moment. Especially things running EF where EF Core doesn't have a particular feature just yet. But EF Core development is cracking on at a good pace.
Telerik and the likes I'm not so fussed about personally. I suppose DevExpress is another one on that list. I think front end component libraries like Prime-ng/PrimeReact are probably the way to go for the future of UI development for Line of Business applications.
Overall I reckon in a couple of years there won't be much of those blockers left at all.