Hi,
I must add a correction to the Michal's reply: our plugins use Qt, but only for specific dialogs, as the Library Browser, Effect's Editor, RailClone Style editor, etc.
But the Max rollups don't use Qt. This is because compatibility with old Max versions.
Qt is included in Max 2019 and above, but we support older Max versions yet. Once we set Max 2019 as the minimum version supported, we would migrate the UI to Qt.
There is not a date for this, since it will depend of the number of customers who continue using our plugins with these Max versions.