Would Mercury be older or younger radiometrically?
Does make one wonder. Also if the decay rate increases could that trigger a nuclear runaway? Could Mercury's (or Venus's) mantle have been partially blown away when fissiles were more prevalent in the past?
And just how long ago was that past??? Makes you think. Of course if the variation was too high then there would be too much heat from decay and the Earth would've suffered a massive melt-down. But, a few years back, the molecular clock dates for the Last Common Ancestor of terrestrial life was only ~2 Gya, even though the oldest life traces were in rocks dated to ~3.8 Gya. Could Earth really be that much younger???
Definitely a line of research to watch very carefully.