Pony Twilight is most likely not going to be in the series again. Think about Pony Twilight's roles in the EQG movies.
EQG - Pony Twilight is the main character, the plot is about her getting her Element of Harmony back from the human world.
EQG: RR - Pony Twilight plays a supporting role, assisting the Rainbooms play a counter-spell and defeat the Dazzlings.
EQG: FG - Pony Twilight is only shown at a small gag at the end where she makes a cameo.
EQG: LoE - Pony Twilight is only mentioned throughout the movie.
EQG: ? - Pony Twilight probably isn't even going to be mentioned. The movie series has become independent. Still, the series revolves around Equestrian Magic. If all of the magic is removed from the human world, it would be very hard for the writers to come up with an idea. EQG was about the Element of Harmony, EQG: RR was about The Sirens (The Dazzlings), EQG: FG was about Sci-Twi turning into a power-crazed demon through magic, and EQG: LoE was about Gloriosa using those magic neck things to turn Camp Everfree into a locked-down nuclear shelter made out of brambles.