Current working assumption is, that the Microsoft support for ActiveX is in it's sunset and will discontinue in a few years totally. Qt 5.15 supports MSFT ActiveX through ActiveQt. Qt 5.15 will be supported up until 2023, and the Qt 5.15 support can be extended for a customer beyond that.
Under this it is unlikely that it would make sense for The Qt Company to bring ActiveQt in to Qt 6. Instead, those needing this support can use Qt 5.15 during the life time of ActiveX itself.