I don't play with domains all day, but this very much feels like nothing important was accomplished, and things are just being made more complicated for political reasons. Sorry if that is being harsh, but I've never had any issue using WHOIS.
If you've ever tried to parse WHOIS programmatically, you'd realize that it being an unstructured blob of text is actually quite unconducive to it being useful. Having every endpoint return a standardized JSON payload specified in an RFC is much better.
All users of the service. Because RDAP has a fully specified format, your client can interpret it in predictable ways and then actually present the information to the user in a consistent format (or be used programmatically). WHOIS is just a blob of text that every service implements somewhat differently, so WHOISing domains across different registrars/registries does not provide a consistent UI, and it's often confusing.
