That said, regular mail is also on the decline, significantly so, as more people use technology instead of pen and paper- bills, letters, contracts, nearly everything is going digital. Packages make up an increasingly significant amount of post office revenue.
That said, anyone who pays attention to Amazon at all knows that they show no remorse about screwing over business partners by entering the same market, and Amazon has been doing that for awhile now.
Even so, I suspect that they aren't going to bother expanding delivery out to where I am now- paying the post office to deliver is almost certainly cheaper than keeping a regular workforce of independent delivery drivers way out here.