First impression after 24 hours of comparing both headphones from an average listener:
Build Quality
Bose are well built, but they feel more fragile than the XM5 (or the QC45 from memory). The ear cups feel shallow and not as sturdy as the QC45 (which used glass-filled nylon). The headphone is really soft, the the lining seems very thin, wondering how it's going to hold. It's quite a small pair of headphones, big head might have problems with the fit. The adjustable hinge are really sturdy and quite hard to move up and down.
Comfort
The QC Ultra are replay comfortable, the clamping force is stronger than the XM5. The XM5 feel lighter on the head. It's a different fit, but both are equally comfortable. I think that the QC Ultra might be more comfortable on longer session because of the wider and squishier headband.
Connectivity
Multipoint works very well from what I've tested so far. I had some problems with the QC 45 stuttering and skipping when connected to both my iPhone and my Macbook, but it's not the case with the QC Ultra.
Sound Quality
Excellent sound quality, on par with Sony and maybe better in the low end than the XM5. It's punchier and more I feel like it has more presence. The output volume is on par with the Sony, the QC45 are quieter in comparaison.
ANC
On par with the XM5 from what I have tested in my house. The Sony seems to have a better passive isolation, but the ANC on the Ultra does a great job of blocking the noise, so they are similar in that department. The QC Ultra has some white noise when nothing is playing, the XM5 are really silent it that regard.
I'm going to compare them further, but right now I feel that there is not enough differences in the headphones for the QC Ultra to replace my Sony WH100-XM5.