Seems like a good idea to me.

If you get the vanilla source from the rosegarden web site, the first thing that happens is the cmake demands qt4.

Disagree !
Just build latest version of rosegarden (16.06) .

CMakeLists.txt
 --------
if(USE_QT4)
   set(QT_MIN_VERSION "4.8.0")

   # Locate Qt4 on the system.
   find_package(Qt4 REQUIRED QtCore QtGui QtXml QtNetwork QtTest)

   # properly set up compile flags (QT_DEBUG/QT_NO_DEBUG, ...)
   include(${QT_USE_FILE})

   set(QT_QTCORE_LIBRARY Qt4::QtCore)
   set(QT_QTGUI_LIBRARY Qt4::QtGui)
   set(QT_QTXML_LIBRARY Qt4::QtXml)
   set(QT_QTNETWORK_LIBRARY Qt4::QtNetwork)
   set(QT_QTTEST_LIBRARY Qt4::QtTest)

else()

   # Locate Qt5 on the system.
   find_package(Qt5 "5.1.0" REQUIRED COMPONENTS Core Gui Widgets Xml Network PrintSupport Test)

   set(QT_QTCORE_LIBRARY Qt5::Core)
   set(QT_QTGUI_LIBRARY Qt5::Widgets Qt5::PrintSupport)
   set(QT_QTXML_LIBRARY Qt5::Xml)
   set(QT_QTNETWORK_LIBRARY Qt5::Network)
   set(QT_QTTEST_LIBRARY Qt5::Test)

   set(QT_RCC_EXECUTABLE ${Qt5Core_RCC_EXECUTABLE})

endif()

----

The default choise is qt5.And if(USE_QT4) is for qt4.
I have both qt5 and qt4 on my sysmtem and the build is qt5.

Sorry for my english.

This bug appears to have been reported against 'rawhide' during the Fedora 26 development cycle.
Changing version to '26'.

This message is a reminder that Fedora 26 is nearing its end of life.
Approximately 4 (four) weeks from now Fedora will stop maintaining
and issuing updates for Fedora 26. It is Fedora's policy to close all
bug reports from releases that are no longer maintained. At that time
this bug will be closed as EOL if it remains open with a Fedora  'version'
of '26'.

Package Maintainer: If you wish for this bug to remain open because you
plan to fix it in a currently maintained version, simply change the 'version'
to a later Fedora version.

Thank you for reporting this issue and we are sorry that we were not
able to fix it before Fedora 26 is end of life. If you would still like
to see this bug fixed and are able to reproduce it against a later version
of Fedora, you are encouraged  change the 'version' to a later Fedora
version prior this bug is closed as described in the policy above.

Although we aim to fix as many bugs as possible during every release's
lifetime, sometimes those efforts are overtaken by events. Often a
more recent Fedora release includes newer upstream software that fixes
bugs or makes them obsolete.

Fedora 26 changed to end-of-life (EOL) status on 2018-05-29. Fedora 26
is no longer maintained, which means that it will not receive any
further security or bug fix updates. As a result we are closing this bug.

If you can reproduce this bug against a currently maintained version of
Fedora please feel free to reopen this bug against that version. If you
are unable to reopen this bug, please file a new report against the
current release. If you experience problems, please add a comment to this
bug.

Thank you for reporting this bug and we are sorry it could not be fixed.