CKEditor has had the ACF (Advanced Content Filter) for >1.5 years now. It allows you to very tightly control which tags and attributes are allowed.
This feature, and the rest of CKEditor has much, much more test coverage to account for the many browser quirks (notably in contentEditable) that they have had to work around, to prevent regressions. It's a waste of time for everybody to solve the same problems and work around the same browser quirks over and over again.
The "Ability to add uneditable area inside editor text flow (useful when building modules like video tools, advanced image editor etc)." feature is probably the only interesting feature. But it's nothing compared to CKEditor Widgets, which does exactly this, and much more (think storing structured content but transforming it to the specific markup that a frontend developer wants). Just compare Wysihtml's "advanced" demo to the CKEditor Widgets demo: http://docs.ckeditor.com/#!/guide/dev_widgets
See http://docs.ckeditor.com/#!/guide/dev_advanced_content_filte... for more about ACF and http://docs.ckeditor.com/#!/guide/dev_widgets for more about Widgets.
And yes, it's open source: GPL/LGPL/MPL/commercial: http://ckeditor.com/about/license
If we'd collaborate more rather than reinventing the wheel, we'd get so much further. One does not just write a WYSIWYG editor…