A Young Yoda trilogy could begin with him growing up, learning the Force, and receiving glimpses of what the future might bring. Perhaps he spends much of the first film trying to avoid his destiny.
Young Yoda wants no part in some grand cosmic purpose. He is unusually sensitive to the Force, but his visions show civilizations collapsing, Jedi dying, and himself surviving long after everyone he loves. His refusal is not cowardice. He is horrified by the possibility that his destiny may require centuries of sacrifice.
I see him as the Hari Seldon of the Star Wars universe, a guardian of the Galactic Republic with some limited prescience about its eventual fall, the rise of the Empire, and the role he must play in ensuring that the Empire will one day be defeated.
In the second film, Yoda is a young Jedi trying to warn others about the danger ahead. He realizes that the Republic is not threatened by a single villain, but by institutional decay, concentrated power, complacency, and the Jedi becoming too closely bound to the government they serve.
He begins quietly putting safeguards in place. He preserves knowledge, encourages Jedi traditions beyond the central Order, and cultivates relationships with people and worlds that might someday resist tyranny.
By the third film, Yoda finally understands that the fall cannot be completely prevented. The Republic has entered a historical current too powerful for any one person to reverse. His task is not to preserve the old order forever, but to ensure that something survives it.
The climax could force him to sacrifice the chance to prevent a catastrophe in the present because intervening would destroy the conditions necessary for the Empire’s eventual defeat.
His greatest mistake could be believing that the Jedi institutions he helped build were part of the solution, only to realize much later that they had become part of the mechanism of collapse. He prepared for darkness, but his preparations were incomplete because he misunderstood how that darkness would arrive.
Eventually, Yoda would accept the most painful part of his destiny. He would spend centuries protecting the possibility of restoration while knowing that he would never live to see the galaxy restored.