I don’t know about New England, but I work for a firm that has offices in Texas and New Jersey. I note that in both places, people under 40 lack a distinctive regional accent. The older ones do, however. In 50 years, Southern and New York accents will be as dead as Latin or Sanskrit.
Incrementalism.
The Air Force requested that I live in TX, MS, MA, and Germany so I became multi-lingual.