Plugins would definitely be the wrong tool for the job for actual new emulator development, but if you needed to do something easy like add an NVRAM for a route

Plugins would definitely be the wrong tool for the job for actual new emulator development, but if you needed to do something easy like add an NVRAM for a router rehost you could do that with plugins e.g. by skipping an instruction and using a callback to implement the desired behavior (as long as it is something a plugin is allowed to do -- you can't access device memory yet).