Wait... Maybe I misunderstood what your said. Are you saying if the material used is aluminum that the heat soak would be worse then the stock plastic intake? If aluminum doesn't cut it like plastic then why are they selling aluminum piping, radiators, intercoolers and coolant reservoir?
To fashion bespoke automotive parts in a plastic mold requires pricey CAD engineering software (and paying a nerd to use it well) even before you start looking into the pricey equipment and molding needs for the actual fabrication, which most won't invest in for a small group of enthusiasts. A lot of vendors sell aluminum piping instead cuz all you need is a mandrel bender which are only a few hundred bucks. Couldn't tell ya if this same logic applies to intake manifolds from a design/manufacturing standpoint.
The premise with an IC or a radiator is that the air/coolant is arriving insanely hot. Hotter than the material itself. That temperature delta allows for heat to dissipate outward and cool the air/coolant. Will the aluminum mani temps be higher than the intake air? imo it may well be. If so, the delta and bigger words than I understand, dictate that the air will absorb the additional heat in the mani. It prob won't be much so let's not make mountain out a mole hill here!
But the heat soak is def more for aluminum when compared to an automotive plastic. Just touch it. You can feel the heat where plastic is barely lukewarm. Now which would you want your intake charge passing through, something already hot to the touch or barely warm? Will it mean that this new part won't show gains? No, it doesn't mean that at all! Temp is not the only metric effecting power. Velocity and volume are also key factors! So if the increased IATs are reasonable, even through the hot mani, the velocity & volume will surely have a positive effect. Will said effect be worth the 500-$2000 this thing may end up costing? Not to me. Unless this mani starts handing our 40 hp gains!!! lol And I highly doubt anyone running a hybrid or S280 is bottlenecking at the intake mani right now....