I was under the impression that the same result could be achieved with Cloudflare, or indeed nearly any CDN. Was I mistaken? Though you may not actually need a secret, private subdomain for static files with all CDNs.
Again, please let me know if I've made a mistake somewhere. I'd love to learn something this morning.
static.domain.com (CDN subdomain with auto provisioned TLS)
static-uncached.domain.com (private pass-through subdomain when CDN is missing a file)
www.domain.com (app server hosted wherever)
You're right that you could do something similar with other CDNs including Cloudflare (you can just set the www subdomain to "bypass Cloudflare" to accomplish a similar result), but I'm not aware of any way to use Cloudflare on a domain without forwarding your nameservers to them, effectively giving them complete control over the domain. At least with Stackpath I can host DNS wherever and simply point the subdomains I want at them.
Also, by the time you do the work to split static files into separate subdomains you might as well go with a dedicated CDN. One of the selling points of Cloudflare is for sites serving everything on one subdomain that they can forward to Cloudflare and get caching without any work.
It requires at least the Business level plan, though.
So in this way it's possible to setup CDN with shared SSL for purely static files but not the app server itself; you don't have to give the keys to the whole kingdom so to speak and it's cheaper than Cloudflare at the basic level.