The problem with SO is SO3. It's ending writes the entire series into a wall.
What SE need to do is remake 3 and change the ending.
Once that is done they will have more creative freedom.
...... That has absolutely nothing to do with the lack of Star Ocean/tri-Ace interest.
Actually I'd say it does.
The entire SO series is 1 connected timeline. Because 3 basically gives that a definitive ending, everything else needs to be worked into that.
This actually does limit creative freedom, and I would imagine also sours potential interest in continuing to develop new games. Where will SO6 fit?
Most probably positions would be between 4 and 1, and between 5 and 3. Those have big enough gaps in the timeline where you could do something, but would that something be of importance to the greater SO narrative? Probably not.
I'd also argue that the SO3 ending is somewhat controversial for the community. Take into account how rubbish SO4 is, and how mediocre SO5 is, there probably isn't a lot of interest from the gaming community either.
Now, I'm not saying that SO6 won't exist. But they either need to redo 3, or create a brand new timeline. The latter is probably better idea since they can treat it like something new and fresh.