The Washington Post is framing this as a potential Ronna McDaniel requirement, however given the RNC under Reince Preibus ended up having the same 2016 pre-debate loyalty demand, the requirement is more likely an institutional Big Club proposal and not the idea of the chair. The board and RNC charter members of the professionally Republican apparatus are the ones creating the litmus tests.
Essentially, you will remember in 2015 and 2016 the RNC demanded that all of the candidates swear an oath to whomever won the GOP nomination. In the first Fox News debate of August 2015, the candidates were told to raise their hand if they were not willing to swear or affirm their intent to support the eventual nominee. Everyone except Donald Trump (and Ben Carson) lied. WATCH:
The construct of the loyalty oath was predicated around the fact the RNC institution did not support an outsider like Donald Trump using their club system to achieve the office of the presidency. Trump was independent minded and held his own platform positions on trade, economics, border security and immigration that ran counter to the approved policy positions of professionally Republican members.link
If you want to understand American politics you have to read Sundance. ABN