Let me restate that: it is not free to continue supporting PGP. It has a tremendous cost both in its own maintenance and its opportunity cost. Every moment spent attempting to mitigate its fundamentally broken design is a moment that could instead be put into designing something new, that works properly and doesn't require dragging around the massively bloated corpse of 1999-era cryptographic engineering.
To me the most interesting part of the article is whether or not the current signatures are even capable of being validated or not, which the answer to that is > 50% of them are not, and those are of the people who care enough in the last 3 years to still be using this undocumented feature.
Is it possible to build a secure signing system ontop of GPG/PGP? Sure. But doing that requires working around or eschewing so many features from it that you might as well just use the base primitives yourself rather than being tied to GPG/PGP.
And then there's the third category, which is "threats which could be mitigated but PGP makes this hard so people tried and gave up." Just giving up entirely doesn't seem like the right reaction here, and that seems to be what the PGP downers are advocating.