You can now enable "loop" on any upload in the player, to have it repeat indefinitely. Just click or tap the loop icon in the player to turn it blue.
As an uploader, you can turn looping on by default. To do this, go to "edit" on the upload, and turn on the option.
Unfortunately, as you may have guessed from second screen shot, loop mode is not seamless at this time. This is due to limitations of audio playback in HTML5. I do not rule out improvements in this area in the future though.