Jack tries to reconcile his commitments to originalism and to living constitutionalism by arguing that originalism supplies general principles that later constitutional interpreters (judges and others) must obey even while they update constitutional rules to reflect changing times. Whereas Scalia-style originalism determines the entire "skyscraper," Jack's originalism supplies only the "framework" of the constitutional edifice; others fill in the architectural details.
Jack's right to think that Scalia's skyscraper originalism is impractical; and, as he notes, Scalia himself recognizes that the court can't, as a practical matter, overturn certain highly established precedents in order to recover the original meaning. But Jack's own style of originalism raises questions as well. The 14th Amendment does not so much establish a principle of equality before the law but, as Jack notes, reflects a compromise between those who held a stronger version of that principle and those whose weaker version permitted what we today would call exceptions to that principle—such as denial of suffrage on the basis of race. In his work on originalism, Jack draws on the principle of equality in its strong form, but on what basis can he ignore the beliefs of those who made sure that the principle would be so watered down, that discriminatory suffrage laws would not be constitutional violations? It is a crooked, ugly framework, but on Jack's view, we are committed to it (and I don't understand how he gets around this problem).
An even more limited version of originalism would treat it as, at best, the blueprint (a word Jack also uses) for the building. In the years immediately after the blueprint is ratified, a constitutional edifice is constructed along the lines it lays out. But as more years pass, new wings are added, the façade is replaced, new stories are piled atop the roof, walls are relocated—and eventually one has an elaborate structure whose origin in the blueprint can be found only by a talented archeologist, in an odd wall here, or some old ductwork there. The blueprint is of antiquarian interest only. The originalist, like a fanatic preservationist, laments the loss of the blueprint authors' original vision and seeks to destroy the structure so that the original modest little country manse can be rebuilt. It makes no difference that the building has evolved to meet interests and circumstances that the original authors never imagined.
I think this version of originalism is truer to Jack's commitment to living constitutionalism. There is no particular reason to look back to the original understanding except in narrow conditions—perhaps to understand an ambiguous precedent, for example, or perhaps to maintain some useful piece of institutional design that is largely arbitrarily but settles things. But why be bound by someone else's principles? The original Constitution's lasting impact results from its role as starting point, and it should become less and less relevant as time passes, precedents pile up, norms and interests evolve, and institutions change.