Some time ago I wrote about the status of Qt-based libs for using the serial port. Some days later I was pointed to the QtSerialPort project. The good news on this is that this is a project aimed to enter into Qt 5.
I have tested the lib with some apps that originally used QExtSerialPort. So far, so good. The license terms seems pretty OK (it wouldn't have got that far in the Qt code review if it weren't).
In the meantime, I received a reply to one of my messages from an upstream dev of QSerialPort (note that is Q and not Qt). He was very kind, but considering the effort to get QtSerialPort inside Qt itself, I think it's better to try to develop with this last lib.
Maybe I should try to package it and upload it to experimental.