Well, sure it's available in the Arch Linux repos. 45 packages depend on it. (Who knows what the Qt devs were thinking.
)
Just upgraded my system, which doesn't include sigil since I built that myself, and Sigil starts up okay without even being recompiled...
...
As it has been established that Sigil does not officially support 5.6.0 (because that would require building Qt5 from scratch to get QtWebKit), there is all of a sudden an unexpected chance that things will break and bleeding-edge distros have issues because we move so fast.
But as you say -- hopefully nothing insurmountable.