It seems to me that custom HF transformers might be expensive, surely far more expensive than off the shelf magnetics.
I inherited one design that used a transformer in a switching supply to put out two different regulated voltages. It worked well enough but I could never get the transformer quiet, it appeared to be sized properly to prevent saturation and regulated adequately just was unacceptable for a studio product PS always singing along. ???
Since the transformer was single sourced and kind of an odd ball, I just backed up to make it a simpler single voltage regulator using a more common standard inductor and added a pass regulator for the lower regulated voltage. Less clever, but dead silent. ;D
I ASSume the regulators are adjustable over a range so common off the shelf inductors should cover most applications, but in my (limited) experience, transformers in switchers are less common, resulting in less favorable price and availability.
JR