> New OS4 software is written in Reaction. There is no need for MUI4.

http://www.os4depot.net/index.php?function=showfile&file=network/browser/odyssey.lha
http://www.os4depot.net/index.php?function=showfile&file=utility/misc/daysleeper.lha
http://www.os4depot.net/index.php?function=showfile&file=game/children/selmasmemorygame.lha

Besides, OS4Depot lists 78 files when searching for "mui" as requirement.