If I could flip a switch and change this one aspect of modern life, I'd be willing to re-learn all my old reading/writing habits. It just makes more sense to "build" ideas upward.
Less of an issue, for sure - but not gone entirely. As someone who takes a lot of "manual" notes with pen&paper, I would still regularily end up with a smeared mess and dirty arms by writing bottom-to-top.
Besides, I don't really see an advantage over writing top-to-bottom. Even the OP only states personal preference / aesthetics as a reason, but no practical use that would make it better than the current version.