As of the 30th July, there is a new release for Nintex Forms for Office 365. With the latest release you can now edit task forms, there is support for multiple attachments, and improved attachment validation.
Read these posts by Nintex Tech Evangelist Alexandre Joly
- Edit Task Forms on Office 365
- Attachment validation on NF for Office 365
- Multiple attachments in a Nintex Form on Office 365