Based on their funding post a few days ago, they’re on a digital ocean droplet that costs $18/month or something, so there’s plenty of room to scale that up. Whether or not they can afford it or get enough donations to keep it up is debatable. Point is the hosting requirements are fairly low.
Umbraco is a fantastic open source project, as well as a great example of how open source can support a profitable company as well, through support, training, and certification programs.
I don’t use it as much these days, as its not part of my day job, and for my hobby projects I’m using static site generators, I appreciate what Umbraco has, and how they do it. It really is great software, for users and developers.