Ok, I'm a gene-engineer by training, and I'll admit I've occasionally toyed with the idea of boosting animal intelligence [otters being and obvious non-primate possibility].

Partly because it would be interesting to see what happens, but partly because nature needs advocates who can articulately state their case or alternatively, smart resistance fighters who can stand up to human encroachment.

There's also the fact that in the process of engineering sentience you could figure out the genetic basis for it somewhat better.