That hardware isn't already there. They won't share a switch, but they will share routers. IP routing with overlapping networks doesn't really work, so you have

That hardware isn't already there. They won't share a switch, but they will share routers. IP routing with overlapping networks doesn't really work, so you have to get creative with e.g. DNAT or proxies. Both of which consumes additional resources, even if the routers can do it, you will have to buy bigger licenses, processors will have more load, etc.