Yes and no. Certainly, some third party company can make a FEL for the new Sig. series (SS) tractor, however, that may void JD's warranty and that company may not care if you break your tractor. I think it is Johnny Products that has a disclaimer that they are not responsible for any damage to your tractor that can result from using their product. So, said third party FEL company, mentioned earlier, could make a a FEL that bolts right up to the existing, unmodified, frame and give you the full capabilities of the 45 Loader of the Ultimate Series (US), but if the frame on the SS is not as hefty as the US tractors (I don't know that this is the case), you run the risk of bending/breaking the frame of your tractor.
Now, looking at it from JD's perspective, if the number of 45 loaders sold was small in comparison to the number of US tractors sold, they may not have the economic incentive to make a loader to fit the new SS tractors. This would especially be true if there were many more 3PH's sold for the Ultimate Series tractors than there were FEL's. JD could reasonably assume that most owners chose the US over SCUTs because they needed a small tractor capable of using 3PH accessories but not FEL capabilities, and from that data they made the SS that can have a 3PH added, but not a FEL. Another issue is that if they did make the SS frames less hefty than the US tractors, then they will have to engineer a workaround to allow them to provide a FEL and still honor the warranty of these tractors. Finally, this could be a way to steer potential owners toward their SCUT's and eliminating the overlap between the HDGT's and the SCUT's.
Of course, I think the jury is still out which way JD is going to go. They could be feverishly working on a FEL for the SS in time for a 2014 release. Some here who have watched JD for much longer than I have, have said that it took JD a year or two to make a FEL for the X7xx series. Unless there's been an official statement from JD, which I don't believe anyone has posted, yet or I missed the thread it was in.
Paul