The 33-year-old South African was not offered a new contract because of the IRFU's succession policy, which seeks to develop homegrown talent.
"I would like to come back to Ulster in a coaching capacity," said Pienaar, who joined the Pro12 side in 2010.
"I would see my starting point as an underage or youth coach."
Pienaar has been a key player for Ulster since his arrival on a two-year contract from Natal Sharks.
The Springbok, who has won 88 international caps, has scored an impressive 877 points in 137 appearances for Ulster.
Ruan Pienaar is leaving Ulster at the end of the season but the scrum-half is already planning to return as a coach when his playing career ends.