Who said anything about getting rid of the Regionals? Thirdrail is talking about the retirement of the current Acela sets.
I didn't specify anything, Daybeers as this is a long way off. However, let me help you out a little bit by translating Just Thinking's theory:
Even limited regional service. Running just few times a day, with a really long train set. With a branding other than Acela. Just to keep the bus people on there toes. One thinks that would be a workable and profitable level of service.
Just Thinking's theory is clear to me. if you have a dedicated, confined train set, on a dedicated corridor that has much more capacity than your existing brand, you can push more people to that service by reducing access your competing brand (regionals). Then, you can use the released equipment to support other routes. In other words, you may only run trains on the NEC that will venture off corridor...and there is nothing saying they have to permit local travel between certain points.
This is a long, long way out but I have the feeling that Just Thinking is quite astute.