a SEP rating has no upper or lower weight limit therefore the privileges of the JAA SEP rating allow the holder of such a rating to fly a microlight aeroplane on the grounds that it is within the SEP definition but, you can't count those hours for JAA purposes because of JAR-FCL 1.005.
Legally, the only differences training under JAR-FCL is for VP Prop, retractable undercarriage, pressurisation, Super charger turbo charger and tailwheel. There are no differences given for microlights!
As the JAA have virtually folded, until EASA comes up with something new, there will be no change.