Following the buildd log chain, the hold-up seems to be build dependencies that cannot be installed. At the base of the list of dependencies is "qtwebengine-opensource-src" for which "alpha" is no longer an architecture listed by the maintainer(s).
Here's the high-level dependency chain: "akregator" depends on source package "kf5-messagelib" which depends on source package "qtwebengine-opensource-src". I'm looking into whether "qtwebengine-opensource-src" is buildable on "alpha", but I suspect this is going to be similar to the "iceweasel" dependency on "firefox-esr", i.e., not easily fixed. --Bob