Judging from BF3 and BF4 there will definitely be differences between last gen consoles and current gen consoles and PC in terms of player count, playable map areas, and even the "eye candy" such as trees, buildings etc due to the PS3 and 360's antiquated technology and very limited system resources.
Mind you this is all speculation but but a solid conclusion based on the differences between the last two games that I've seen playing on all 3 platforms in BF3 and all 5 platforms in BF4.