They're working on their stretch goals now (the odd values are due to their goals being based on GBP):
$660,240 - In-game music recorded from historical Medieval works (already met)
$825,300 - Full orchestral score
$990,360 - Playable prologue/tutorial quest line featuring a female character who rescues the main player character (essentially an introduction/backstory they already have planned, only the player will get to do it themselves)
$1,155,420 - Performance motion capture, but full-body and face
$1,320,480 - TBD
$1,650,600 - TBD
The developers have already announced they'll be releasing modding tools for third-party content, but no word has been made yet about multiplayer. If it's not already planned, that could conceivably be one of the TBD goals.