The DC-DC converters used in the common VV and VW mods are mass produced for all sorts of things. They are usually amp-limited to 1.5 or 2.5 ampere.
Now there are two types: The ones that pump up the voltage first and then hack it down to the selected voltage (These are used in mods that use a single battery) or those that can just lower the voltage, but not boost it (Those are used in mods with stacking batteries).
The type with stacking batteries may be able to put out the 30 or so watts you crazy people want, but the chip would be larger. The reason for that is two fold: efficiency of the chip and size of the internal printed connectors.
Those circuits have about 90% efficiency, which means that there will be >3 watts heat (at 30 watts) heating up the tiny little chip. That is a lot. Then, imagine a tiny wee little silicone piece that needs to control 30 watts with a printed connection smaller than a hair.
Rob might be able to tell more, but the VV REO chip might actually be able to handle a sub ohm coil, but I am guessing it is amp limited (and thus resistance limited) to warn about shorted atomizers.