There are probably a half dozen platforms that we could declare 'good enough' and stop all major R&D in. Maybe some changes to the interior/self driving systems as those are being researched for EVs anyway. Maybe some minor tweaks to the internals as issues are identified at scale. The design and production is good today, and it wouldn't be a major loss if they represent the height of consumer ICE while EVs take over.

A large reason why car manufactures update model lines is to comply with updating emissions, efficiency, and safety regulations. This is the environmental condition that forces major model refreshes.