I think this could be right but does one person can really handle both the backend and the frontend projects when the frontend becomes a first class project from day 1 instead of a kind of afterthought? In other words: a single developer can start a Rails+jQuery sugar web site in N days. Where he would be with Rails(API)+React after those N days?

Another question. I checked those rails+react gems. The pro is that they put everything inside the Rails project. The cons is exactly the same. Even in the case the same person is doing both jobs, shouldn't we acknowledge that they are two separate projects and work on them separately?