sudo pacman -S merkuro 
error: failed to commit transaction (conflicting files)
merkuro: /usr/lib/qt5/qml/org/kde/akonadi/AgentConfigurationForm.qml exists in filesystem (owned by kalendar)
merkuro: /usr/lib/qt5/qml/org/kde/akonadi/CollectionComboBox.qml exists in filesystem (owned by kalendar)
merkuro: /usr/lib/qt5/qml/org/kde/akonadi/MobileCollectionComboBox.qml exists in filesystem (owned by kalendar)
merkuro: /usr/lib/qt5/qml/org/kde/akonadi/libakonadi_quick_plugin.so exists in filesystem (owned by kalendar)
merkuro: /usr/lib/qt5/qml/org/kde/akonadi/qmldir exists in filesystem (owned by kalendar)
merkuro: /usr/share/qlogging-categories5/akonadi.quick.categories exists in filesystem (owned by kalendar)
Errors occurred, no packages were upgraded.

Probably Kalenar should be in conflict with Merkuro?

I swore I added all the needed provides/conflicts/replaces to new merkuro (replacing kalendar), but checking the commits, it is not there.....
Rebuild will be up shortly, and include to needed automated kalendar removal.