> The expression of the shared environment in the womb would be reasonably expected to lead to epigenetic correlations in twins at a crucial stage of development where they would have the highest impact, without them being heritable.

Sure, but that wouldn't be relevant to twin studies because both twins would be exposed to the same environment.

The pop culture discussion about heritable epigenetics tends to assume influence outside of in utero conditions or crossing multiple generations. It's where the "generational trauma is in your genes" idea came from.

We're discussing twins raised apart. They're not necessarily in the same environment (except during gestation).

It would be relevant to twin studies. Specifically, separated twin studies, where shared environment is assumed to be negligible. If the developmental impact of epigenetics is significant that won't be true.