If my post caused confusion, apologies! I know of no confirmation for VI, I am merely working on conjecture, as the series is over a decade old now and had its most recent release just a year or so ago in NA, I'm not seeing any real reason to doubt it.

As for setting, my best guess would be Kooluk. If it's not, I'd say it'll be somewhere pretty left-field and unlikely; either somewhere we've not heard of before, or somewhere oddball that we know almost nothing about, like Kanakan or Zelant. I don't think it'll be New Armes mainly because they obviously weren't reformed before V, and after the events of V they're said to have become more moderate and friendlier. Though obviously later on there could be a reaction against this But I think Kooluk is the most likely setting 'cause it's pretty well established to be in a pretty poor state. I'm not sure Harmonia will ever be the subject of a Suikoden; if it is then I'd say not until very late in the series.

Edit: And oh god yes you must play Suikoden II.