Moving TableExt into custom tables is Microsoft's suggestion from performance point of view. Technically not difficult, for many document tables the feature TransferFields helps to copy (all) values into other tables. If we start using custom tables, we must need to extend all processes where TranserFields is used. Many events are already provided, but missing a process is risky.
A new table event OnAfterTransferFields would help to skip subscribing to many additional events and assure full process integration.
procedure CopyCustomTable(var Rec: TableB; var FromTable: RecRef)