>>28029436I felt the same way about mega evolutions. Some of my favorites didn't get a mega, and it's a bummer.
But I imagine if they tried making synchro evolutions for all Pokemon, it would be absolutely crazy hard work for them. If synchro evolution is a thing, it's probably something exclusive to special Pokemon, Pokemon with an elevated status. Starters definitely fit the criteria, and Rockruff would be special indeed if it got to share this ability with them.
Rockruff could be a secondary starter of sorts, if that's the case. We've been given secondary starters before (elemental monkeys in gen 5, kanto starters in gen 6).
Besides, the Chinese leaks (which have proven to be the most accurate and consistent of all leaks), state that Rockruff evolves into a werewolf. They do not mention split evolutions.
So the rumors and speculations of Rockruff having split evos depending on your chosen starter may not be real.
These are all just my thoughts and opinions though.