Certainly not something to be dismissed out of hand. Decay rates of a few nuclides have been known to vary for other reasons. 7Be is a fairly well known example. The 0.0765 keV IT decaying isomer in 235U is another. Anything that decays by EC is obviously igoing to see decay rate changes if the atom is completely ionized.
This study is interesting because it deals with alpha and beta decay which occur entirely within the nucleus.