There are clues that Google is working to merge the two products
Google has been adding new features to Drive and has been pushing the service towards something that warrants its name, the Google Drive, but it may be getting ready to make one of the biggest moves yet by making Gmail attachments a part of Drive.There's no official word yet, as has been the case before, Google itself provided a glimpse of the feature in action in a GIF posted on its Drive Google+ profile. Google usually tests new features with employees before enabling them for the rest of the world.
What's more, mentions of Gmail attachments have been found in the Google Drive source code.
As for how it would all work, it's probably fairly simple, the Gmail attachments section will list all of email attachments you've sent or received, all of which are stored by Google anyway, making it easier to find and work with them, like you would with any other file in Drive.