Besides TextUI.modelToView() and viewToModel() operation the View API should reflect specific aspects of editor view hierarchy such as lazy construction, non-EDT view rebuilds which implies a requirement for locking.
View SPI should allow to register custom view factories to build client's custom views.
When designing the editor.lib2/org.netbeans.modules.editor.lib2.view package I have assumed potential API/SPI classes. They will need some polishing but it should be more or less like this:
*** Bug 213999 has been marked as a duplicate of this bug. ***
Should this still be opened?
Yes, although we'll probably have to postpone to 7.4 in order to rewrite current side bars and other code to verify that the API will cover all the necessary usecases.