I'm sure the reason why Honda stayed with the 1.5L for the new Si is because of budget. Honda already has the 2.0L N/A and 1.5L Turbo for the regular 2017 Civic models and the Type-R having the unique performance 2.0L turbo. That's already three different motors for the 2016-2017+ Civic trims. I don't think Honda wanted to put more R&D for a new performance motor. A de-tuned 2.0L from a Type-R would have been a good choice, but not for Honda's marketing perspective. That will more likely damage the Type-R sales because the customers will see that the Si will be more bang for the buck. Honda's approach for this year is to sell the first ever U.S. Civic Type-R. I don't think Honda cares at all if the Si sales decline.