Even when using server side paging some requests can be very long, and may be canceled by the user. Adding a CancellationToken parameter to the ToDataSourceResultAsync.
Align more to grid items (since treelist is essentially a grid with parent/child). Need a ForeignKey element to allow for helpers etc. instead of forcing override and manual Templates.
columns.Add().Field(n => n.StatusId).Title("Status").Width(150).Template("#=statustemplate(data)#"); columns.Add().Field(n => n.CategoryId).Title("Category").Width(150).Template("#=categorytemplate(data)#");
ForeignKeys should be treated the same was a grid elements and allow for the UIHint, etc.
Full alignment of the .Add function to .Bound in grid would be nice as well, but naming is as critical as the functionality.