i think the reason why they won't continue from suikoden 3 is that they need to tell more stories prior to that year. once that is done then we'll see yuber and pesmerga fight as a subplot to a story based on Luc's theory. but are we sure that Luc is dead now?
there is so many untold stories yet to be done.
I dont think Konami plans to tell us everything. Look at one of Suikox questions to Konami:
Question #5: If Suikoden Tierkreis is the future of the series can we expect to get any form of resolution to the unanswered questions of the old series?
Konami: It is too early to say but it will depend on how the games progress in the future, but we would like to resolve many of Suikoden’s mysteries.
They would like
to solve many
(not all) of then. In my interpretation, they will only explain what is most essencial to the story.