Well, it's not the worst fan theory ever, & I suppose it's possible, but I'm not feeling it. It's not as if the whale language would necessarily be a galactic universal among other planets' whales, such that it's at all likely the probe's intelligent life were whales simply because they spoke it. It's much more likely imho that they have their own language, whatever they are, & that they have translation going on, so to understand & communicate with Earth's whales.
The notion that they'd actually be whales is so far-fetched that if it were true, then it'd be just as likely that they are native Earth humpback speakers, & in that case it's just as possible that Earth's whales were actually of the same species from their origin world... which all seems really silly, considering homosapiens had been allowed to cause their extinction. You'd think if there were a direct link like that, between the probe intelligence & Earth's whales, that wouldn't have been allowed to happen.
Nah... I just always assumed it was an alien race, looking for signs of any language being used on Earth, at a time when the only one was whales, predating humans quite a while, made contact, kept the channel open, & when it stopped coming due to extinction, an expedition was sent to find out why, & it took until Kirk's era for it to arrive, some 200+ years later. After all, they didn't seem bothered by the number of whales speaking it having been reduced to 2. I'd imagine a spacefaring whale race might be kind of bothered by that
Which makes me wonder... We now know they have a language. Even Spock could meld with Gracie. It would be kind of cool to find out what developments that yielded, having made contact with a species on Earth itself, that predates humanity. You'd assume humans would be trying to figure out that language themselves now
