This question came out of a discussion with a friend who's into futurism, but imho doesn't understand pet owners--he doesn't think there'd be much of a market for longevity dogs. On the other hand, maybe I don't understand pet owners, so let me know one way or the other.
My question about the distinctive look is based on the assumption that if you're optimizing one group of traits, you probably don't get to be picky about other traits so longevity dogs will probzbly look like small or medium-sized mutts. The other reason I'm interested in the effect of no visual markers is that you don't get automatic bragging rights by having what looks like an expensive longevity dog. I'm assuming that they'd be small or medium-sized because I've heard that large breeds tend to be short-lived.
Alternatively, if the tech exists to make longevity dogs, maybe it'll be in place to give them a distinctive appearance as well.
My notion is that you could tell whether you're getting a longevity dog by having the puppy tested before you buy it. If you've fallen in love with the puppy but it doesn't have the longevity gene(s), it doesn't cost as much.