Why does the arcade suddenly get faster?
The developer explains that the demo arcade deliberately accelerates near the top score, making the trees fast enough to stop the player getting onto the leaderboard. The sudden difficulty spike is part of the described demo behavior.
Is the target 9999 points?
Do not assume 9999 is a confirmed target. A recorded demo scoreboard shows PINE at 999, SPRUCE at 998 and ASPEN at 997. The player’s YOU:13 result is an ordinary score, not proof of a special high-score ending.
Is there a high-score secret ending?
There is no confirmed high-score trigger or special-ending procedure to follow. The developer’s acceleration explanation tells you why normal leaderboard attempts are blocked; it does not establish that every possible secret is absent.
Treat instructions that promise an extra ending from an unspecified score or “all collectibles” with caution. The described arcade behavior does not provide such a rule.
Will the arcade change?
The developer expressed a wish to rework the arcade for the full game. That is a plan, not a description of an already released replacement.