This would be an incredibly entertaining legal quagmire to watch unfold.
Pressure for Acceptance
There is already pressure against confining certain animals (dolphins, chimps, whales, etc) in labs that are perceived to have high intelligence. When one of them gives an interview on CNN, there’s going to be a little more chaos. It’s heartbreaking to see the physical characteristics of confinement and abuse, but to hear an animal describe the experience of being experimented on is going to be difficult for many people. And it’s going to scare a lot of people.
Animal rights activists will have a heyday with this. Seeing animals speak english and have near-human level thought, even with artificially enhanced intelligence, is going to seriously affect the public’s attitudes toward all animals. People will be having some second thoughts about their hamburgers when a firsthand slaughterhouse experience suddenly sounds like Auschwitz. It certainly won’t sway everyone, but the increased empathy for animals will undoubtedly become a driving force for change.
Research opportunities could also be greatly enhanced by giving uplifted animals personhood, returning them to the wild, and observing and cooperating with them. The ocean in particular is far too large for us to adequately study safely. Imagine uplifted sperm whales that could explore the depths or the opportunity to examine what type of complex society dolphins form. Seeing high intelligence in a multitude of species could give us invaluable insight into the nature of intelligence and how physiology affects behavior
Pressure for Denial
There are some human beings who, through severe disability or injury, could be said to have even less intelligence than some non uplifted animals. Legally, these people are all still treated as persons (including those born without the capacity for normal intelligence) because personhood is rarely (if ever) about intelligence. It’s about being a human being.
Whether we admit it or not, humans very much like having dominion over planet Earth. Earth is often referred to as ours. The impact on human society of uplifted animals, especially in large numbers, could be profound. Almost all animal product industries could be catastrophically impacted. Personhood for uplifted animals is a slippery slope to either treating all non-uplifted animals in the same fashion, or a push to uplift as many animals as possible. These are terrible outcomes for massive and very politically powerful industries across the globe.
Ultimately, I suspect that this would become less about personhood, and more about usage of the uplifting technology. Seeing animals with such a high level of intelligence would scare a lot of people. There would likely be a major push to release the existing uplifted animals from research captivity, but it would be tremendously difficult to decide what to do with them next (how torturous would it be for a dolphin of human intelligence to be the only one of its kind?).