I think it's pretty much cuz they aren't in great quantity to make it to collections.
I see them only rarely here.
I've held one half grown one, he was fine didn't bite, but was very active, which I think is typical. Since they were a breed I was thinking about getting, I've done a little research on them.
I don't recall any negatives or special problems in owning one.

www.a1pythons.com/savu.html

I had a pair of Savu's some time back. The female was horrid, the male was a doll. As far as their ability to be kept, it all depends on their background. I never had a problem with mine, they were easy keepers and active eaters. They are pretty active snakes, nothing like a nice docile ball python :) If your friend id just starting out with reptiles, then I would say, go with a more tried and true species...if she has had other species and wants something a little different with a high activity level, then go for it :)