Waiting a year and either beefing up the specs or lowering the launch price would help in some ways, but I don't think their decision to launch Scorpio late 2017 is solely based on their wants and needs. No matter what they say, strategy is key. It's a big part of why PS4 has done so well.
PS4 has won this gen, end of story. The longer this gen is aloud to go on, the longer XB has to wait to get back in the game. The sooner XB can launch their next gen "no generations" console, the more pressure they put on PS to move on to PS5. Now PS would most likely want to stretch PS4 as far as it can possibly go, but if XB can come up with something much more compelling now, with specs that Pro can't come close to competing with overall, than PS is somewhat risking next gen by holding onto this gen for too long. That's not to say PS5 would have to launch immediately, but may be pushed forward quicker than PS would like, if Scorpio sales are impressive enough.
By waiting another year, they also take a chance on being compared to PS5 instead of PS4 Pro. Right now Scorpio will look much superior to Pro. If they wait, and small leaks start seeping through the cracks, and PS5 is said to be stronger than Scorpio, and not all that far off, than it will put a damper on the Scorpio launch and its sales. Something XB most certainly does not want. XB needs to launch at a time where they can better control the marketing and message and not be as affected by the competition. Again, strategy.
