In the original script that made it to early animation, it was revealed that the Son was being influenced/mentored by the spirits of Darth Bane and Darth Revan from the EU.
The one-man Jedi jumpspeeders are based on speeder bike concept art conceived for Star Wars: Episode VI - Return of the Jedi (1983).
The beginning of "Battle of the Heroes" from Star Wars: Episode III - Revenge of the Sith (2005) can be heard briefly just after the Son takes Anakin's lightsaber.
The 'Jedi fortune cookie' message that opens the show reads "He who seeks to control fate shall never find peace"
The logo on the entrance to the temple is a Sith symbol.