AFAIK it is alpha for several reasons:

python3 is one and pyside not ported to qt5 and probadly will not. gpodder harmnattan uses pyside+qt4+python2. so there is some stuff that need to be solved to make it for sailfishos...

if harbour will support python its probadly python3 and possible pyotherside.

maintainer, thp, is working on jolla atm so I guess he has lack of time working on gpodder atm.