Unless Ho-OH or the original Mewtwo crossed paths within the Horizon story, I couldn't imagine a rational reason for Ash to meet the RVT if it serves no purpose to progressing Ash's goal.
Ash may have defeated the current strongest world champion (Leon), but he's never defeated or befriended one of the strongest pokemon (original Mewtwo) featured in the main story of the anime.
I'd imagine that if Ash were to appear or cross paths with Liko and Roy, the event would need to coincide with his pledged goal of becoming a Pokemon Master.