The images in the original post seem interesting, had they been able to realize those as actual sets on TNG. But the idea of dolphins exchanging in conversation with Picard, no matter how sincerely acted on his part, would've come across as Ludacris. It would've been laughed at, by the general public. I do not see how it could've been handled, or what purpose dolphins would've served onboard.
How the hell could you ever evacuate these dolphins, without use of the transporter, if an emergency ever came up, of if the ship was set on self-destruct and the window for escape was very limited. Answer: it would've never come up. We would've never seen it. Fans would bring it up, but it would never be shown, because there's no point. It's expensive, and it adds nothing to a story that isn't specifically about them. As a visual, an interior set, it would've been striking, just to have an aquarium of that size onboard. But it's probably best left to novels, anyway.
How the hell could you ever evacuate these dolphins, without use of the transporter, if an emergency ever came up, of if the ship was set on self-destruct and the window for escape was very limited. Answer: it would've never come up. We would've never seen it. Fans would bring it up, but it would never be shown, because there's no point. It's expensive, and it adds nothing to a story that isn't specifically about them. As a visual, an interior set, it would've been striking, just to have an aquarium of that size onboard. But it's probably best left to novels, anyway.