Khem... QtQuick is not really designed for time critical tasks. Queued connections are the least of your problems.
QtQuick is just a QML plugin. I want to use QML as a language to define an object tree of any QObjects. The app could be a deamon with no UI.

I'm not even going to explain now what that is Wrong(TM).
What do you mean? That's what direct connections are for - slot is executed by the same thread which emits the signal.
Direct connections are used when necessary. The UI elements are connected with other parts by queued connections which makes sense because I don't want my UI to disrupt my real time part (UI runs under dedicated thread anyway).

You can expose an alternative for Connections that will make direct connections
How is that possible?

Either way, using JavaScript with garbage collecting, JIT compiling and all that stuff for time critical tasks is very likely bad design.
The application doesn't contain only time critical parts. Javascript gives user an extra flexibility. Let say I need to add some extra logging to my app. I can just write handler which will do logging in QML without recompiling my app. I am fully aware that Javascript handlers run under dedicated JS engine's thread.

I just need to have a choice which connection type to use. Real-world applications usually need both.