Plane travel, as it usually appears in D&D-like settings is not a component of the Sea of Stars but that does not mean that they do not exist on some form or another:
Worlds Beyond the Sea of Stars
After the gods were deposed and the world Sundered, access to the other worlds became exceedingly difficult. It is believed that the Empress sealed the worlds beyond away, while the gods who ruled them had been slain, many of their servitors survived, now impotently sealed away in their paradises and pits. The beings of the worlds beyond could still be brought though into the world by use of spells and rituals but rarely for long. The previously existing gates to the higher and lower worlds beyond were shattered and destroyed immediately after the Sundering as the dragons seized and plundered the churches and temples. Those that have opened pathways to such places have been able to cross over but none have ever returned.
Sea of Stars RPG Design Journal 