Why not add Pufferfish and Pufferfish+ (a faster version than standard pufferfish) as a server software?
Pufferfish can handle about a lot of players, and Aswell is a fork of paper, it has much better performance than paper (since really it's like purpur but better than Purpur yeah I don't know)
- An async entity tracker that allows entities to be tracked in a separate thread, freeing up the main thread for other tasks.
- An async pathfinding algorithm that allows mobs to find their way around more quickly.
- A number of other optimizations that improve the performance of various Minecraft features. (you already know).
I'd really like to see it on Aternos.