Actor Allusion: Sort of. Tracey Moore played the unicorn Cheerilee, and later Mayor Flitter Flutter, so even if Cheerilee is very different now, you've still got a city run by Tracey Moore.
Early Draft Tie In: One of the specials featured Fiesta Flair, a pony who was ultimately canceled and replaced with Candy Apple. Despite being canceled, she still appeared as background pony in G3.5 as well.
Name's the Same: Toola-Roola's a reverse-Cheerilee/Cherry Blossom situation: there's a toy-only previous G3 Toola-Roola, whom she resembles only in name.
Older Than They Think: Pinkie Pie's ability to appear in multiple places at once and break the fourth wall didn't actually start in My Little Pony: Friendship Is Magic. The former appeared in the second webisode "Pinkie Pie's Ferris Wheel Adventure", and the latter came about as early as "Star Song and the Magic Dance Shoes" before G3.5. Her "Pinkie Squink" is also a predecessor to G4's "Pinkie Sense" though they both work slightly differently.
What Could Have Been: Fiesta Flair, a character who appeared in the short Pinkie Pie and the Ladybug Jamboree never made it into toy form. Word of God says that due to her Mexican accent, name and symbol there might have been backlash that caused Hasbro to rethink her development. It's telling that toy-only character Candy Apple is 100% identical to her with the maracas turned into, well, candy apples.