Doable, but asking for a monumental failure imho. If they released a new console pretty much 2 years after the PS4 pro, they'll be offering really terrible value in terms of longevity to customers. Less than 3-4 years is going to push people to thinking a PC and just upgrading the graphics card every 2 years is a better option(and it is).
If they wait till at least late 2019 they can beat Scorpio performance by a larger amount but risk as with Scorpio vs PS4 pro and PS4 vs Xbox one, launching at the wrong time. If MS release a new console again a year later with a significant performance boost they are screwed again.Xbox One had non impressive sales because everyone knew the PS4 was 50% faster, which led to more games rendered at 1080p or with higher frame rate. Basically the majority of games give a superior performance on PS4 and it became the clear sales leader, by a mile.Scorpio will now be the same, 50% faster than the PS4 pro and everyone knows it. MS will obviously market that if you want higher frame rate or higher resolution there is one choice, they'll literally say they made a mistake on the Xbox One and say that is why they knew they needed more power. They'll market the very reason the PS4 won as the reason to choose Scorpio and not make all the same horrible marketing choices with the Xbox One which had to be changed last second.
Personally I would say due to the cheapness of development with semi custom, the second they realised their console was going to be so vastly underpowered they should have started moving to a new chip for it. They could have ended up 6 months later than Scorpio, but with the same or maybe marginally more power. Instead while the Pro comes first, everyone already knows the Scorpio will flat out trounce it.
Sony also made a big deal about turning off half the chip for 1080p, about not offering better gaming for 1080p... huge huge marketing mistake, horrible in fact. If they just said hey, this one will do 4k with similar performance to the PS4, or will make certain we can achieve 60fps in 1080p it would attract far more buyers. That they won't offer a smoother higher frame rate 1080p is a joke and is actively going to put off a huge number of buyers. So PS4 pro will be out first, but everyone knows it won't be the best console and by a large margin. If MS now market sensibly, drop any gimmicks, focus on gaming and market about higher framerate at 1080p or 4k gaming (with still 50% higher performance than PS4 pro) then most people will wait for the Scorpio and of a 3-4 year cycle Scorpio will win, hands down.
Sony have already marketed PS4 Pro as 33% slower than Scorpio and offering zero benefit at 1080p..... bad hardware AND Xbox One scale terrible marketing/design choices, how did this happen. Seriously if a year ago they found out Scorpio would be 50% faster or suspect it they could have started not even from scratch, just the work to replace Polaris IP blocks with larger Vega IP block, either HBM2 or 4 more gddr5 chips for more bandwidth and they have a Scorpio matching chip, a 12-18 month delay but that puts them maybe 6 months behind Scorpio. Horrible horrible decision to keep going.