Above is the link to the blog. It's a type where you need to register with some site to comment, and strangely there's only one comment.
I'll translate the entry into English (I'm a native speaker of Japanese):
The Birth of Tierkreus
"What is Genso Suikoden?"
It was decided that a sequel will be created,
and this was the first question I thought about.
108 stars, an HQ, a story that is not good vs evil, and a story that has continuity. There's probably many more components that make a game "Genso Suikoden."
All of the games take place at some time on the same historical timeline, and are connected in some way... that's the charm of the Genso Suikoden seires, so we should continue that story. That sort of comment was made repeatedly in our initial discussion.
However, is that really acceptable?
Doesn't the world of "Genso Suikoden" have greater possibilities?
Aren't there things we are held back from doing because of all the history that exists?
Can't a new story be created while keeping the story that has been created over a span of 10 years?
The answer to that question was the "Million Worlds" (infinity), and the creation of Tierkreis-- not merely as a side-story, but as a new saga.
After that he goes on to describe game mechanics of Tierkreis so I won't bother translating it, but this entry is from 2009, so it is a while ago. Perhaps he may have changed his mind since, but at least this was his original perspective.