POPLmark seems to generally be considered solved. There are multiple good solutions using different tools for all of those problems, I believe.
And the real goal has largely been reached. At this point, if you're proposing new PL theory and you don't have a mechanised proof of it, the entire work is viewed with considerable skepticism.
That said, reuse and productivity are still not much better than that of real-world software. My peers who do that sort of thing are in very high demand for post-doc positions on projects funded by various governments/militaries to "prove the X property about software system Y."
And the real goal has largely been reached. At this point, if you're proposing new PL theory and you don't have a mechanised proof of it, the entire work is viewed with considerable skepticism.
That said, reuse and productivity are still not much better than that of real-world software. My peers who do that sort of thing are in very high demand for post-doc positions on projects funded by various governments/militaries to "prove the X property about software system Y."