How to successfully use RDAP protocol instead of whois

Direct short answer

The answer to "How to successfully use RDAP protocol instead of WHOIS?" is: there are no way to successfully use RDAP, only, perhaps, to try some experimental implementation... But even experimental, I not know how to try it.

Answer to your wrong hypothesis

The URL that you used is wrong, so, in part, your question details started with wrong hypothesis.

The domain RDAP.ORG is not an "official authority", it is a owned by a commercial organization, so it is a false ".ORG". There are a footer at rdap.org pages acknowledging that is no offcial service, and is a tau.uk.com playground. Try some RDAP client.

Best interpretation and long answer

This ICANN report of 2015-12-03, "Registration Data Access Protocol (RDAP) Operational Profile for gTLD Registries and Registrars", have some clues, some history, ... and fished with

(...) it is premature to include a requirement for all gTLDs in the RDAP Profile (...) A call for volunteers is planned by January 2016.

So, no one decides to enforce RDAP on all registrars... And there are no "call for volunteers" announced this year.

Dream with an intermediate alternative

The main problem with WHOIS today is the "free interpretation" of the published information. There are no "standard Rosetta stone", but we can start one (!), to offer a maturity intermediary for RDAP.

2019 news

Starting 2019-08-26 it will be an ICANN requirements (hence for all gTLDs) to have an RDAP server at registries and registrars.

From https://www.icann.org/rdap:

RDAP Timeline

gTLD registries and registrars are required to implement an RDAP service by 26 August 2019. ICANN org continues to work with gTLD registries and registrars to implement a service-level agreement and registry reporting requirements for RDAP.

Read more on RDAP timeline at https://www.icann.org/resources/pages/rdap-background-2018-08-31-en

2020 news

RDAP services are working! You can try it in a RDAP client (as old whois client) or directelly in the top-level domain authority's API. Examples:

• Authority's RDAP API endpoint of the top-level domain .com is https://rdap.verisign.com/com/v1/. For example the Brazilian's UOL.COM is described at https://rdap.verisign.com/com/v1/domain/uol.com .
• Authority's RDAP API endpoint of the top-level domain .org is https://rdap.publicinterestregistry.net/rdap/org/. For example W3C's domain is described at https://rdap.publicinterestregistry.net/rdap/org/domain/w3c.org
• There are many RDAP clients working fine, the OpenRDAP.org is one. You don't need to know the authority or its RDAP API endpoint, is direct.
  Examples: rdap -v uol.com or rdap -v w3c.org.
• Online clients also can be used. Examples: client.rdap.org resolving uol.com or openrdap.org resolving w3c.org.

Entity transparency: the transparency policies are local. For example UOL.com.br is registered by the .br authority, and Registro.BR obligates that all domain name owner must to be revealed (see CNPJ entry). Check it by a good and universal client, like OpenRDAP, rdap -v uol.com.br.