That's probably true.
But I would think the relevant question would be whether he would have rejected radiometric dating, since that is the subject of the article. I don't think an assumption that because he would reject one means he would have to reject the other is valid.
Neither is that my assumption at all, dear tacticalogic!
The two are not at all directly comparable. One — Darwin's theory — is based on a speculation regarding the historical evolution of the biota which some people find "intuitive" and "emotionally satisfying."
Seems to me this has more to do with proving Nietzsche's dictum — "God is dead" — is correct than with showing how species actually evolve. Plus it goes without saying that historical events are precisely those which are not known and cannot be known by means of direct observation. But genuine science must stick to the latter.
To the extent that radiometric dating relies on direct observation, and can be validated by replicable experiments, Newton probably would have approved of it.
But bear in mind that Newton had no knowledge whatever of relativistic and quantum effects that bear on the behavior of material bodies. And it is also true — as Alamo-Girl and MrB have already pointed out — that a fundamental presupposition WRT radioactive decay rates is that they are "steady" and uniform over time. But if actual observations indicate that this may not be the case — the thesis of the article at the top of this thread — then on what principle does this presupposition rest?
Newton's sublime work describes the behavior of material bodies at all scales, which he expressed in terms of mechanical action. But he was the very first to say that any mechanistic system would generate and accumulate errors over time, which would tend to "derange" the systems so described. Implicit in Newton's work is the idea of Final Cause, otherwise known as purpose or goals operating in Nature: For Newton allowed that God himself would have to step in every now and then to set matters aright again, to restore the order of material systems over time.
Compare this with the Darwinist belief that biological systems evolve by chance + selection. Looking to the logic of Newton's reasoning, it would appear that he would say instead that living systems evolve according to their Limit (the Aristotelian Final Cause) and not ever by "pure, blind chance," as Jacques Monod put it.
Anyhoot, back to the problem of radiometric dating, and its expectation that decay rates are steady and therefore predictable. This may not be the case.
A similar problem for physics these days is that, even though the expectation is the expansion of the universe proceeds at a steady rate, recent observational data indicate that this expansion has actually accelerated in "recent" times. Which tends to show that the expectation of a steady expansion rate has no basis in observational fact. Likewise, recently observed anomalies in the behavior of material objects in the vicinity of the event horizon of black holes do not conform with expectations (scientific predictions).
It seems to me that physics itself has bumped up hard against its own self-imposed limitations, the most critical being the banishment of Final Cause from its field of study, which was arguably the entire point of Francis Bacon's scientific revolution.
Science retains the other three Aristotelian causes: Formal, material, efficient. But Final Cause — again, which deals with purposes, goals, limits in Nature — is totally gone from its permissible methods.
In my very humble opinion, science has to being back Final Cause if it expects to make any further progress. It seems to be at a dead end without it.
It seems to me that issues of relativistic and quantum behavior could be further illuminated by the reintroduction of Final Cause to science.
JMHO FWIW
Thanks so much for writing, dear tacticalogic!