I don't think Naoshi will be making a season two because he feels its complete the way it is. Having another season without Kaori just wouldn't sit right with me. However, there is an OVA about 8 year old Kousei or something like that. There is also an extra manga called Shigatsu wa Kimi no Uso: Coda which is a bunch of short stories about 5 year old Tsubaki, 14 year old Nagi and stuff like that.