It would also make is possible for larger companies to attest to purchases made and / or the quality of participation within their community. Imagine a scenario where I donate $50 to an open source project using GitHub Sponsors with my domain as the identity and GitHub attests to me spending that $50.
Over time, it would be possible to demonstrate a significant "investment" in your domain validated identity and it would be done by spending money online like you normally would without any additional cost. The attestation that you spent the money is simply a side effect of something you're already doing, but it's a really good indicator (over time) that you're a normal participant.
At the very least, I think having a domain as a globally usable handle would help to reduce impersonation which is a serious, difficult to solve problem right now.