Wohoo another Honda that cant keep up to the competition. Oh well. That Civic Hatch sport with 180hp is a decent package now that it basically has the same engine as a Si lol.
We don't know what the performance will be, so kind of hard to dismiss it right now. If two years ago someone told you the new Civic will come with a 1.5L, you might have laughed. Well, the current regular Civics can be faster than the old Si's, and much more efficient too.
As far as moddability, my guess is that Honda does not want the Si to cannibalize the Type R sales. If the Si comes with a detuned R engine, then for a few thousand more you could get it to R level. Considering the Si and the T are both targeting enthusiasts, they want the R to offer a distinct advantage, in this case it seems like the displacement is the key thing.
It could also be that the 2.0L would raise the cost of the Si too much, it might only be a performance engine with more expensive internals and production costs.