Aviation Week says the only time a multi-billion dollar procurement of a new presidential aircraft is possible is the last years of a president's second term. And so, the Air Force is expected to issue a request for proposals this fall. The proposal is open to all, Europeans included. But nobody expects the Americans to buy a foreign-built aircraft for such a publicity heavy role, so Boeing will get the job. Boeing will offer a new model 747-8, which is somewhat bigger than that of the aircraft in service. Wingspan will increase from 195 feet to 225 feet, length from 231 feet to 250 feet.
Boeing and GE are doing some work on defenses already. They are looking at mean to suppress the IR signature of the engines in order to confuse heat seeking shoulder launched missiles. Presumable there will be something like Common Missile Warning system to see the flare of missile engines, warn the crew, trigger the flare dispenser, and perhaps aim an IR laser at the incoming missile to dazzle its seeker head.
Price humungous. They are talking about $1.65 billion in just "research and development". As part of the R&D program they will buy one aircraft. The Air Force declined to estimate the cost of all the electronics or to estimate the total program cost to procure the second aircraft, in flying condition. Guess it would be another couple of billion or so.
The current Air Force One's have been flying since 1987, which makes them middle aged as aircraft go. They are younger than the B-52's which are still flying combat. Unlike cars, aircraft never wear out. As soon as anything shows wear, or fails, it is replaced. The air crew will refuse to fly an aircraft that isn't in tip top shape. A couple a hundred DC-3's, built in the 1940's, are hauling passengers to this day. And there is nothing in an aircraft which cannot be replaced. They replaced all the wings on the C-5s some years ago.
If it was up to me, I'd just keep flying the current aircraft. I might be willing to fund some electronic updates, but other than that, I'd fly 'em another 25 years.