As a heavy user of Drupal, I can say that I have encountered this more than once in my work and we have found the solution that Drupal provides to be pretty robust. There is a switch on every post that can be toggled for the type of input format or markup. Various input format plugins are available to support various styles. We have typically had to either highlight this feature in the UI or focus heavily on it during training to get good use of it though. Typically we set the most basic filter and allow more advanced filters as needed. There is also a drupal module that allows for user selectable defaults. I wonder if there is anyway to inexpensively incorporate something similar with Evernote?