Domestic rats are very fragile genetically, it would be nice to try to "fix" them. Also science knows a lot about rat genome so it would be even easier than dogs.
There's actually a huge problem with pet rats in that they're all remarkably inbred. If you don't get your rats from a dedicated professional breeder who's been at it for decades, your pet is likely going to get really sick at the end of their life. Females tend to get catastrophic tumors, and all have extremely delicate respiratory systems. Out of the dozens of rats I've kept, only one died quietly in her sleep of old age. The rest were horrific and gruesome.
Yeah, there'd be a good amount of money in it for whoever can fix rats' genetics.