I'm sure most interior designers would take those into consideration; form follows function. As for metal going hot or cold, have you forgotten that all cars use metallic seat belt buckle clips? I've been stung many times. Metal is usually not used because of a) contractions and expansions b) weight c) simplicity of molding plastic vs metal. However, using anodized aluminum, which is lighter, is better than painted plastic from a luxury perspective. Also, the contractions and expansions can be calculated and adjustments made to avoid disastrous effects.
If I wanted fake metal plastic I would buy a cheaper car. However, I'm buying a Lexus therefore if something is meant to exhibit the characteristics of metal, it better be metal not painted plastic. Would you accept it if you went to a Michelin star restaurant, ordered crab and was served some simulated artificial garbage?
Not to repeat myself, but again, I drove several German competitors (and a few lower-tier Japanese competitors to Lexus) and to varying degrees, many of the models exhibited the problems listed above. So clearly, those designers in those cars did not fully take into consideration all of the above aspects. Otherwise I would not have had the hassle I did driving those models. Sure, all cars use metal seat belt buckle clips, but not all luxury cars have the entire seat belt piece completely metal. It's usually a plastic surround which encircles the metal buckle. A few brands I believe may have all-metal surrounds.
I won't pretend to know on what basis metal is or isn't used in luxury cars, aside from obvious parameters like cost, weight, contraction/expansion. I have heard anecdotally that in the past, Lexus has been very conservative about using large amounts of real metal in an interior, due to the problems above that I myself have observed.
You misunderstand what I said. I am not against the idea of real metal itself. Obviously in a real luxury car I prefer real vs. fake materials. With that said, I would prefer real metal
only if that brand has taken the extreme and utmost care to alleviate the above-observed issues. This is simply my personal view on it. Some may not agree of course. If the above-noted problems cannot be alleviated, then I would rather real metal not be used, rather an alternative material be used, preferably an alternative that is a real material itself.
Finally, in my own humble opinion, I generally do not like metal trim in an interior, regardless of whether it's real or fake metal. I personally much prefer wood trim over metal trim, or simply any sort of soft-touch trim.