Is any company going to actually deploy this system, in, let's say, two years?

You can trust Helix and Perforce because they have been doing this for decades, and this is part of their core business. You know they will keep maintaining the products for a while.

But for Epic, they could give up on this project tomorrow, and nothing will happen to their business. If anything, they'll get some dev resources back which helps their business.

It's like why anyone would trust Cloudflare to continue investing in EmDash over the long run. Cloudflare doesn't care about CMS. Their business is not providing the best experience for readers/authors/site owners. It's just a side hustle that is almost irrelevant to their business.