In Season 3 Episode 7, Wonderbolts Academy, Spitfire tells Rainbow Dash:

"You're no wingpony, Rainbow Dash. You're a leader."

This didn't mean much to me at the time, but upon reading the Wonderbolts Academy Handbook and rewatching the episode, this line took on a WHOLE NEW MEANING for me. From the handbook:

"A LEADER is a pony with a high rank. A high rank has authority and control over a team's structure and function. A leader has a great deal of applicable experience and is knowledgeable on an assortment of relevant subjects."

After this are descriptions of TEAM MEMBERS (Wonderbolts who left the reserves and become a part of the team) and CADETS (what Dash was before Firestreak retired). In other words, this line from Spitfire may be foreshadowing that Rainbow Dash is not only destined to be a Wonderbolt, but destined to be a LEADER of the Wonderbolts.