I doubt it. I feel like if Grookey were showing up soon that would've been spoiled by now.Well maybe Grookey can debut in the lab og prof Magnolia?
Like how Sobble and Korrina were spoiled in advance before they actually showed up.
With Grookey it's just been Radio silence. No promotions, isn't on the poster with Eevee, Dracovish and the rest, and etc...
I'm sure that they'd be hyping up the debut of the final Starter to appear in the show