The python3.4-rm transition is pretty much over . python 3.5 development continues to chug along.
Today reports of problems with anki and calibre programs are popping up in #debian-next. I can confirm an install of calibre 2.55 (i386) in Sparky will result in calibre - well read the bug report
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=827922
same report errors as on my atom netbook. I have done prior "apt autoremove" which has purged python 3.4 on 3 bare metal systems with no noted problems. Bug is listed as "grave" and if you have apt-listbugs installed it will warn you prior to installing.
Note: To pre-existing installs (LXQT) in sid(uction) and a pure debian testing LXQT the calibre launch is not affected and calibre continues to work.
EDIT: I am not using the Calibre 2.60 blob direct from Kovid. If you are you might get this http://www.mobileread.com/forums/showthread.php?t=275615
The debian maintainers of sigil and calibre have been fantastic. It would be way too much to backport the newer versions to stable as both programs are under heavy development and utilize python3.5 and Qt5
Interesting for the future about qtwebkit and it's replacement in 5.6 as testing is already at QT5.6.1 is
http://www.mobileread.com/forums/showthread.php?t=270258
EDIT of course the revision to 2.60 fixes this.