More than an HTML wrapper
The OWA app should be more than a simple HTML wrapper. It does not even support all features available in a mobile browser (see: Options), let alone a desktop browser (how do you create/rename/delete folders? not possible, because not possible in a mobile browser).
S/MIME support would be great. But this is technically not possible as long as it is only an HTML wrapper. Because of this, many suggestions in this forum are also not possible.