some new details are here
 - i like to think their manes start to flow and glow and allthatstuff only then they using magic like Twi did in Tirek's episode.
 - luna has light-blue lock of hair as a part of NM design
 - luna's wings are long and narrow so she flies like sea birds - long time and for long distance. 
 - tia has more wide and short wings so she's quite fast and quite maneuverable.
 - tia's wings are colorful from the outside and luna's from the inside.
 - older sister is taller and more chunky ;) (Wink) but they're both still bigger than regular pony 
 - luna has claws on her wings and she uses them all the time to climb or grab things