The texlive-latexextra package is outdated (I've flagged it) because the exsheets package is updated (with a new features!). I want a simple version or maybe git-version. I think it should be an AUR package but how can I handle the file-conflicts? I don't want overwrite exsheets.sty and I think it isn't good solution.
Is there any solution?
So your proposed exsheets-git would conflict with texlive-latexextra (and it should be in the conflicts array). So you could not have them both properly installed at the same time. If you want the newest exsheets, you could make a aur package with all the newest components of texlive-latexextra. Then it could conflict with and provide that package, so you'd install your new one and remove the other.
This would be even easier than making a brand new aur package as you could just get the current PKGBUILD from the ABS and modify the exsheets source url.