I'm guessing Panthalassa appears in umamusume is gonna be another Silence Suzuka fan.
While Panthalassa didn't directly appear (for now), a Panthalassa reference was made at Twin Turbo's good-ending in the game, co-hosted by Kita-chan in a complete reference to the same Tenno Sho. In a twist of heart-warming fate, it wasn't even a week after Shishou was added to the game when Panthalassa won the Saudi Cup...
That's not TRUUUUEEEEEEE!!
No!
Panthalassa's going to run with Turbo!!
But this creature looks like it wants to run with me...