I've been playing with Wayland on my Arch Linux box, and a lot of stuff is actually working pretty well. I've noticed a slightly odd behavior, though: some text and widgets are larger in a Wayland session than in X. This seems to apply to the Plasma splash screen, the bottom panel and its menus, and some (but not all) Qt apps. For instance, System Settings and the Wireshark Qt GUI have the widget issues, but Amarok doesn't, which makes me think that it could be a QT5 thing. I've tried using the "Force fonts DPI" option in System Settings, but that doesn't seem to change the text size even when I restart applications. I'd like to find a fix if I can, but I'm not sure where to start. Are there any Wayland-specific configuration options hiding in one of the config files?

EDIT: QT5 applications running under Weston don't seem to exhibit the same issue, so it's definitely Plasma-related.

Put "export QT_WAYLAND_FORCE_DPI=[desired DPI]" in your .bashrc, log out and log back in. Should be fixed.