It is cool to see these, and it is one of my favorite sequences in the novel as it was portrayed there, however it's probably better we did not seen it for two reasons.
Firstly, as I see it, the film is as it is pretty much at optimal length, the perfect point where it doesn't seem too short or too long. Adding this in would've needed like another 10 minutes of screen time, if not more? At the worst case scenario, some existing sequences might've been dropped in favor of it, which would've been tragic. If I had to choose between the Gallimimus scene and this one, I much rather have the Gallimimus as it's compact as well as shows T-Rex as real predator hunting other animals. Not monster like the sequels have tended to portray the carnivores.
Secondly, considering how poorly the animatronic T-Rex handled water, it could've been a total disaster to try to make it work. Yes they probably would've constructed third model altogether on top of the other two, but I'm not entirely convinced it'd looked that great. Also, T-Rex sitting and sleeping... it is difficult for me to imagine how that could've looked great? Just looking at those storyboards, and even imagining the scene in the novel when it's sitting there, I see it as pretty awkward. Probably not translating well to screen.
As for adapting this for JP5 or JP6... really hope not. Time of adaptations from Crichton's material has way passed IMO, TLW should've been the final time for that. Let's finally do something original and not hang into old strings. And in any case, we sort of got river scene in JP3 already, although heavily modified and not as interesting (and without the sleeping bit). Finally, this sequence fully in CGI doesn't strike as exciting, especially if it's that JW level of over exploitation