This is just wicked cool.
Reddit user Berdu has used a mod created by JJxORACLE that replaces the blimp in GTA 5 with the Reaper Ship from Mass Effect 3.
You can check out his complete set of images over on imgur. Of if you want higher resolution images, hit up his Flickr page.
The Mass Effect 3 Reaper as Blimp v1.01 mod is currently in beta, but you can download it over on GTA 5 Mods.