Must have somehow missed this information, but BF4 will feature a proper Spectator Mode - at least it's confirmed for PC. Here's what they've showed about it on their extensive streaming coverage from their 64-player booth at E3.
Being a huge fan of Battlefield montages, this will yield a lot of greatness to behold. Hopefully the feature will make it to PS4 as well. I might finally get around to do my own montage.