Actually its even premature to even contemplate a name for "this fetish." Is it even a fetish? Which definition or "fetish" are we even talking about? One definition (the strict one) of a fetish is some ordinarily not-sexual object, situation, or element that must be present for a person to be able to engage in sexual behavior. I have personally met hundreds of people who found quicksand to be interesting or sexually stimulating in some way but I have met exactly one who claimed it to be necessary to sexual behavior.
Ehh...It really depends upon the individual. Kind of like the guys that like their wives or girlfriend to dress up like french maids, in leather, like a playboy bunny, etc. Some do it occasionally because it's fun and adds a new element to the sexuality. Some do it because they're bored with regular intercourse with their partner, some because that particular look peaks their interest in that way, and maybe a few because they can only be turned on by that look. That's really the problem in trying to categorize and label anything having to do with sexuality, you can't overlook the individual psychological factors involved in each person. I like using the dog model. Three guys both like dogs as pets. They have a deep respect and admiration for canines, and all three agree on that. But one likes beagles, another likes Great Danes, and the third likes Chihuahuas, so they never get along about which dog is the best, and calling them all "dog lovers" to their face seems impersonal and generalized to them.
With me personally, it's the dramatic quality of the scenario, even a bit of loving the element of danger. Very few things I've done in terms of work or pastime lack a certain degree of danger or risk. So quicksand for me is another extension of that, and one that can be shared erotically with a special lady or in my fantasies. But I digress.
I doubt we'll ever answer the original question. This is really fun though, delving into the psychology of all this. I've thought it all over quite a bit over the years, but I didn't know anyone else was. Heck, I didn't really think I'd be able to have conversations like THIS when I joined up. I'm really glad to have met you guys.
For straight-up love of sinking in quicksand, I would chose katapínophilia- the love of being engulfed. And its twin would of course be katapínophobia- the fear of being engulfed. 
