Been digging around for a while, and still haven't found one. Wonder if anyone made it yet?

No, no one has made one to the best of my knowledge. I imagine it would be a bit tricky, but I invite people to try if they want.

I believe it would be possible as a mod, and potentially as a program if GeoSquare's In Game Timer is anything to go by, what things would you want it to split for? Most events beyond those you receive achievements for would be difficult to autosplit without mods I would say

I guess you could split like TheeSizzler, when he enters the Nether, exits the Nether, enters the End, and wins