When I heard the announcement, I was hoping that inserting files from Google Drive would be the solution. However, it isn't. It is only inserting a link that does not allow you to open the file, but always lead to Google Drive in a browser... So, it does not provide editing capabilities on iOS, nor on the Mac or Windows.
I use it in a similar way, so that I'm able to work on a budget spreadsheet on several devices. ... execpt iOS. It is not possible to directly edit an attachment on iOS. It would be possible if Evernote on iOS provides a document provider presenting your notes / notebooks and attachments in the way the initial poster suggests.