Probably by design - or just not implemented yet - but it seems the flags for the RazorFormat plugin are missing.
I am especially keen on seeing the MinifyHtml and UseAdvancedCompression added to the .Net Core version.
One idea might be to use https://github.com/Taritsyn/WebMarkupMin/wiki/WebMarkupMin:-ASP.NET-Core-1.X
This could work, but it does not play nicely with ServiceStack by throwning a ‘NotSupportedException: Stream does not support writing.’ exception. Not sure if this is ServiceStack causing this or the WebMarkupMin package…