The main problem with BlueGriffon's source view is the following one : tabs disappear in source view... In other words, to copy some markup from one document's source to another, you have to switch back to wisywig mode. That's an ooooold thing: Nvu and Mozilla Composer already had that very same restriction and that is caused by our nsPlaintextEditor.
But since Bespin is now used by BlueGriffon for the source view, I can probably work around that restriction. Let me think a bit about it