Late for this but I will give my input
If Matthew is still the main character, then more than likely, there will be a cutscene involved that forces the party to get passed Mount Aleph and into the Europe looking portion of the Map, with a boat gained rather early
If not, then I don't know
Now for changes, we now know that "Europe" exists, we will probably see the continents East of Gondowan start to change into a form that resemble the real world a little more, with Indra looking like its going northward, and Osenia breaking up.
Hesperia and Atteka could have a land bridge between the two to resemble the Americas, but who knows really
The northern reaches probably won't be so northern this time
It is possible GS4 will pull off some event near the end of the game that somehow causes the World to become round, and give an explanation of the demise of Alchemy and Psynergy to tie it in to our world (the world being round would make the need for Alchemy become moot)