Only parts of Qt that are required for KDE are upgraded in KDE neon. This causes some serious issues. Musescore and Calibre can only be installed via the developers' AppImages and installers, respectively, due to an error with qtbase-abi-5-5-1 being a virtual package with no candidate providers. This is minor because as I said, there are workarounds.
I can confirm having this issue. I think this is unfortunate and the workarounds not great options. I specifically also have the issues with MuseScore and Calibre specifically. I hope this will be fixed.
*** Bug 384512 has been marked as a duplicate of this bug. ***
This have recently reappeared in Dev Unstable edition where all qtbase-dev packages were forcefully uninstalled by apt dist-upgrade and now while I'm trying to reinstall for example qtquick1-5-dev it outputs: Investigating (0) qtquick1-5-dev [ amd64 ] < none -> 5.5.1-2build1 > ( universe/libdevel ) Broken qtquick1-5-dev:amd64 Зависит on libqt5declarative5 [ amd64 ] < none -> 5.5.1-2build1 > ( universe/libs ) (= 5.5.1-2build1) Considering libqt5declarative5:amd64 0 as a solution to qtquick1-5-dev:amd64 9999 Reinst Failed early because of qtbase-abi-5-5-1:amd64