As others have mentioned there are already places that will finance or lease pins.
I think the first true X-as-a-service we might see in pinball is Software-as-a-Service (SaaS), where you can pay a monthly subscription and have access to the library of games that work on your machine, a-la multimorphic or even potentially deeproot. Subscription tiers giving you access to different levels of content.
This would be a significant infrastructure investment to do it properly with 100% uptime, so I think it's currently beyond the reach of smaller players. deeproot might have the pockets for it though.