"do you think they are going to make the games on each system separately and not port the games from xbox to ps4"
There isn't a snowballs chance in hell of them EVER making the games for each system seperately because it would at least triple the time/effort/work required to develop a game.
I highly doubt that Activision will break their business partnership with Xbox, especially with the way they have completely screwed other platforms over the years (which caused many to abandon their platform of choice to switch to Xbox) Not to mention Microsoft has alot more money to tempt Activision with than Sony does, and as anyone knows the ONLY thing Activision cares about is making as much money possible with the least amount of time/effort spent.
My prediction: Unless the next-gen Xbox console is a complete disaster, CoD (along with many other titles) will continue to be made primarly for Xbox and ported to other platforms for many years to come. (which is unfortunate as Xbox is the worst platform IMO)