The NCBI have added Access-Control-Allow-Origin: * to the eUtils response headers, to allow cross-origin resource sharing.
This means that anyone can now make client-side PubMed search interfaces, like this one.
Only the eSearch and eSummary methods have the Access-Control-Allow-Origin header so far, so it's not possible to get abstracts or full citation data this way (using eFetch) yet.