If Honda have spent all of 2015 producing another pup that can’t be fixed until 2017, then the fallout will be immense.
McLaren have struggled for sponsorship as no-one wants to put their name on the slowest car on the grid, plus Ron Dennis has staked his personal reputation on a turnaround in team fortunes. Alonso may well decide to take a sabbatical for 2016, scaring off even more potential sponsors.
For Arai to be “promoted” under such circumstances would be highly unusual, I suspect that the real quality of the power unit is better than first feared, but not quite as good as first hoped.