I'm relatively new to K2, but conceptually I have played around with creating a single form to handle those modes. The general approach is to have the separate display, edit and new forms/views generated by K2 for SharePoint as a reference. Then you copy either the edit or new form and view to be the starting point for your combined one. After that, you essentially need to copy the rules from the forms and views of the other modes into your copy and add rule conditions so that the display rules only execute when in display mode, edit rules in edit mode and new rules in new mode. This is a brute force method and is time consuming, but it forces you to become familiar with all the rules/details that K2 for SharePoint generates for you. I imagine with more experience going through this approach, you would then be able to come up with a streamlined combined form/view from scratch.