You mention that Polymer is "sticky" and likes to only work with other Polymer elements. Since Polymer 3 is built on LitElement, shouldn't it have the same base level of interoperability as LitElement? Or do you see Polymer 3 elements that somehow have functionality regressions over the base LitElement?
Polymer 3 is a mostly mechanical migration of 2 to use ES modules.
Polymer 2/3 both use the class-based method of inheriting from a base element, but they use Polymer-isms (such as the notify stuff)
There's no real relation to Lit, aside some of the same authors.
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