Oh i agree that a car doesnt have to be as light as possible these days, but the extra weight of a milled ally chassis ( which this new 503 is ) verses a carbon one will be very minimal.
Cost of a milled & anodized ally chassis over a straight carbon one ? Again minimal - in fact the carbon ones would probably be cheaper.
Heat dissipation, well possibly it might help a tad, but i cant remember ever having problems with over hot motors anyway in a carbon chassis - in my 501x & DB01r they run quite cool - just have good ventilation and a motor heatsink
Stiffness.... hmmmm again maybe, but a) does the TRF 4wd platform NEED to be any stiffer ? The 501x and 511 are already very stiff... And b) not so sure about being more durable in the real world. Ok the ally chassis might not break or shatter like a carbon one would do so you might be able to finish the race you are in, but if you have hit something that hard it will definitly be bent or at the very least tweaked. And thats my main bug-bear with ally chassis in general. Once they are tweaked its impossible to get the car set up again properly. It might not be broken in half like a carbon one, but its then got to be replaced anyway.
Better handling being ally instead of carbon ? Maybe, but you would have to do back-to-back tests to confirm or deny that one and on different tracks. Marc Rheinard might be able to tell them apart, but im a very average driver so i very much doubt i would notice the difference on a double-decked 4wd chassis tbh !
Anyways enough of that as it doesnt really matter - it looks to be a very nice car & its a TRF so im sure we will all buy it no matter what its made of
I just hope its not too expensive and spares back up is decent...