That would require re-implementing GameplayKit's agent system (GKAgent, GKBehavior, GKGoal and related classes). It certainly wouldn't produce the same result as GameplayKit, since Apple doesn't provide source code so there's some amount of guessing involved as to how things are implemented exactly.
I'll leave the idea for now, even though it would be a tremendous undertaking with questionable value (by end of 2016, iOS 8 install base will be negligible). I do find it intruiging to have a system like that, because of how inflexible certain aspects are in Apple's implementation.
That looks like it might be comparable just by glancing over the code, although it's a surprisingly small amount of code. Not sure if I'm totally overestimating the amount of code for a system like this or whether it only has a minimal feature set. Nevertheless it looks like a good starting point or reference, thanks for sharing it!
The TilemapKit Roadmap is yours!
All the ideas and discussions
GameplayKit: Agents/Steering bevahior without iOS9