If the film were releasable in its present state, don't you think that Twilight Time would be all over it?
Maybe? Not to knock TT but the ratio between films they've released that already got quality DVD releases vs films that never got a proper DVD release (in R1) newly released on blu-ray is heavily skewed toward the DVD retreads. Sure we occasionally get Fox releases like Centennial Summer, Swamp Water, and Pony Soldier and I love them for at least trying to tread into uncharted home video territory, but the reality is we only get 3-4 new to DVD/blu-ray Fox titles annually, tops. They're more the exception than the majority. As such, it would appear TT is very selective among which of these handful of wildcard titles its willing to bet on each year. Is Boy on a Dolphin a significant enough stand-out to catch TT's eye? Who knows? Being color + Cinemascope possibly gives it at least some edge.
So unless TT is specifically eyeballing this particular title over a thousand of others that never got a proper DVD & blu-ray, and the stars alight to bless it with an acceptable HD transfer, it's most likely not going to happen for quite a while. We know Fox isn't likely ever going to release it themselves, so hopefully TT, Criterion, or even a new dark horse in the home video scene picks up the ball in the future with this and other movies in its situation.