The concept you are looking for is called "Design for Repairability". Its a very old concept that may cost automakers more upfront in designing vehicles for ease of maintenance and collision repairs during ownership cycle. This costs OEM upfront, but saves owners money down the road:
www.wsj.com
Jack A. Ribbens, Designing for Optimum Damageability, Repairability and InsurabilityHow Repair Costs Relate to insurance Costs, SAE Transactions, Vol. 103, Section 6: JOURNAL OF PASSENGER CARS (1994), pp. 1380-1396
www.jstor.org
Some OEMs do it better than others.
Tesla, arguably, does the worst job of them all in this category. As witnessed by the frequency of vehicles getting totaled from relatively minor accidents, and the resulting insurance rate premiums we pay on our EVs.
Mega-castings will push this trend further in the wrong direction.
As you consolidate individual components into larger aluminum mega-castings, and damage to those castings is likely to become terminal to the vehicle.
Currently, any damage to the battery tray in a Tesla totals the chassis. Mega-castings in the front and rear of the car (or a truck) will likely extend the same treatment to the larger proportion of the vehicle.
Mega-castings may make manufacturing cheaper, at the expense of subsequent inability to repair the damage down the road.
It is an unfortunate trade-off.