I suppose this is more practical than the Lightning-to-1/4" phone plug adapter I instinctively built when I noticed Apple's headphone adapter fit comfortably inside a run-of-the-mill 1/4" cable-mount jack (of the sort found on the sink end of a headphone extension cord).

I've also idly considered doing the reverse with one of my iPod shuffles, i.e., incorporating the shuffle electronics into the shell of a 1/4" connector; trouble is, the shuffle runs USB through its four-conductor headphone jack, and 1/4" TRRS connectors are thin on the ground (AFAIK the 1/4"-ish TRRS aviation jack is physically incompatible with ordinary headphone plugs).