Wit a bit of luck & patience we might get usable Qt5 from the PyQt project (in the form of PyQt5). It can already be built against Qt5, but does not currently support QtQuick (both 1&2). Unfortunately there are a few issue with using PyQt vs PySide

• no QtQuick support & not timeline for it (hopefully shows up soon)
  • PySide does not currently support Qt5 at all and there is no timeline. Sfiet Konstantin said on IRC he'll try to at least build QtCore so we'll see.
• no packages for Maemo, Mer or Nemo
  • PySide has ready made packages for Fremantle, Harmattan and Nemo
• incompatibility with Fremantle and Harmattan - if PyQt starts to be used, backports to Maemo might get cumbersome
  • Unless the application either abstracts the PyQt and PySide difference or PyQt5 is backported to Fremantle and Harmattan
• licensed under GPL - requires your application to be either also GPL or to purchase an expensive commercial license
  • While most Python applications on Maemo & co are open source, it might still limit some developers.

All in all, it's quite an issue, as it means both more work for Python devs, wasted effort for those who already ported their apps to the current Sailfish and also that #unlike on Fremantle and Harmattan, Python applications will not be first class citizens on Sailfish, at least not initially.