Thanks for the responses Leti. I would love to see evidence on epigenetic changes associated with breastfeeding - this seems very plausible to me but I do not know the empirical evidence. The developmental period with very rapid changes in epigenetic patterning- which was important in Weaver's overall hypothesized mechanism -- is different for humans than rodents as well, so I do not know how the breastfeeding ages map onto that period.
With respect to GxE, Jason Boardman has articulated interesting theoretical perspectives on how genetic resources may interact with environmental context. The frame you mention is most consistent with 'fundamental cause' theory in that if you have high SES, you can use these resources to escape or avoid the health implications of adverse genetic profiles. This makes a lot of sense to me but it's really an empirical question. At this point, I do not think there is a lot of compelling evidence for us to draw overarching conclusions about how genetic risk and environmental risk interact. I think it's a rapidly unfolding area and would love to see more rigorous health disparities research to help understand how environmental resources offset or exacerbate genetic risk.