The package calibre-bin (required by calibre), unfortunately has a qtbase-abi-* dependency on the QT version it uses. The current version of Calibre in dasyatis is still 2.48.0+dfsg-1b2 however and depends on the qtbase-abi-5-5-1. Migrating to the latest version from Debian unstable (2.55.0+dfsg-1) would make Calibre installable again, since that version depends on the current qtbase-abi-5-6-1.
Actually, this is part of a bigger issue... The chain is:
binutils -> gcc-5 -> python3.5 -> python3-defaults -> pyqt5 -> calibre
We should fix this rather soon, a busted toolchain on i386 isn't great.