my prediction is that the Xbox One version will either have no splitscreen or limited splitscreen for 2 players while Series X will have 4p splitscreen.
also in the campaign there might be loading where there is none on Series X.
Exactly this. I remember Doom 3 on the original Xbox. It's a marvel of porting - running just 64mb of DDR RAM, they squeezed most of the game in to it. They did this by chopping it up, shrinking the levels, to fit inside that tiny memory footprint. If the open-world rumours are true, then I suspect we'll see loading screens and breakup on the XBone versions that simply isn't present on the Series X.
Gonna be so good. I’m confident in the performance as well. Even though halo5 wasn’t the best looker, I’m happy they prioritized frame rate over graphics