That will only make the GOP move to jettison the remaining conservatives (fiscal and social).
A third party takes decades to build. The GOP would love to be allowed to move left and merge with the “moderates” of the Dems.
They love to have a pretend opposition party, they know that it keeps them in power whichever side wins.
I read about some African dictator who was forced to allow democracy, so he created a law that funds opposition parties and soon there were so many he won re-election easily.