The only reason I like to have a huge capacity is to carry a whole bunch of music (~40GB) and/or some movies to watch on the plane.

Spotify is replacing the former use case for me (Google Music is currently not available where I am), but the second stands.

--edit-- Also I'm loving the phablet form factor, which is keeping me on non-nexus at the moment.

How often do you fly? You should be able to hook up a USB key to the Nexus 4 with a USB OTG adapter. Not pretty or horribly convenient, but a it works for occasional use.

If you fly often enough that the second is an issue, couldn't you just get a small tablet for that purpose?

Once you're carrying a small tablet that can make phone calls, why bother with a separate phone?

There is that, yes!

OTOH the use-case was pretty plane-specific, and you don't often need a phone on a plane. Perhaps a 7 inch tablet (to replace the kindle) would suffice. Though then we run into the same problem, the Nexus 7 has no SD slot either!

FWIW I've given up on a dedicated device for that use case; my 11" ultrabook-like (Samsung NP900X1B) can play a much wider range of videos (and also games, coding etc.) and is small enough to be comfortable on a plane. There's a very small space where I'd want a 7-inch-type device (on my way to/from a club is pretty much the only use case I can think of), but I'm not sure there are 7-inch screens much better than a big phone screen.

(personal experience, probably different for other people)