Hi Jason,
Thanks for contacting Syncfusion support.
We will support .Net Core 3 Preview 5 for Syncfusion Blazor component which will be available in our upcoming Volume1, 2019 SP1 release scheduled on May 15, 2019.
We currently working on Blazor documentation improvement since Blazor team changed the Syntax, and the documentation will be refreshed on online 20 may ,2019.
Please get back to us if you require any further assistance on this.
Regards,
Jesus Arockia Sankaran S